Soccer and Physics

Ben, an adult amateur player, asks:

Why does the air pressure affect the distance the ball travels?

Answer

Interesting question – ready-made for an answer chock full of equations and lots of physics, but we’ll I’ll rein in our enthusiasm and try not to get technical.  The answer depends on what the ball is traveling on.

When the ball is in continuous contact with the surface of the pitch (i.e., it is rolling), the pressure of the ball determines the rigidity of the surface of the ball (higher pressure = more rigidity) which in turn has a measurable though not easily visible effect on the total surface area of the ball that is in actual contact with the ground’s surface.  At higher pressures, the area of contact is smaller (because the ball is “rounder”) and thus there is less friction on the passage of the ball across the pitch surface.  There is a smaller, secondary effect at higher pressure caused by a somewhat greater “lift” that makes the ball ride a bit higher on the pitch surface.  Remember, a ball is, in effect, a type of balloon – the more air there is in it, the lighter it is and, as with “roundness,” this reduces slightly the contact surface area.  In short, a higher pressure produces a speedier ball, all other things equal.

However, the other medium on which a ball travels is the air.  Here, again, air pressure acts similarly (see above).  A rounder ball (a function of air pressure)  encounters less “drag” while in the air and has greater buoyancy.  There is a third factor regarding a ball traveling in the air that is not found when a ball is rolling on the ground and that is the fact that, inevitably, a ball in the air comes down and makes contact with the ground.  Holding all other factors equal, a higher ball pressure makes for a higher bounce (a factor that you can often actually hear by listening to the sound of the contact – a ping rather than a thud in extreme cases!).  Now, however, something else comes into play (no pun intended) and that is the angle at which the ball is traveling just prior to contact with the ground.  It isn’t speed as such (as is the case with rolling) but it does directly affect distance – which, in a soccer game, may be just as important as the speed of the ball.  With higher air pressure comes greater bounce when the contact occurs – the more acute the angle, the greater the distance for any given air pressure as a result of the bounce effect.

So, the higher the pressure (within the range permitted by Law 2, of course), the greater is the rolling speed and the greater the rolling speed, the longer is the distance the ball will roll (assuming someone from the other team doesn’t stop it!).  This generalization also assumes a relatively constant consistency in the surface (one of the reasons why, again all other things equal, soccer balls travel faster on artificial surfaces relative to grass, and faster on short grass than taller grass).  Further, for a ball launched into the air, the higher the pressure is, the greater the distance traveled both before and after “the bounce” for contact at any angle of less than 90 degrees behind the ball (disregard all forms of spin … it gets too complicated).

There — not a single formal physics lecture and no equations!  Instinctively, though, a home team which has been coached to engage in fast play will likely provide the Referee with game balls at the upper end of the allowable pressure range.  A different team, which may not like or be used to fast play, is likely to provide game balls at the lower end of the pressure range.  It is not the Referee’s job to deliberately favor one team or another by changing an allowable ball pressure up or down based on personal preferences.  If it is in the allowable range, leave it alone.  If it is not, give it to the home team (it’s their ball anyway) for correction but be sure to check a corrected ball again and, again, leave it alone if it is in the allowable range.

Brief (Sort of) Offside Answer

Jeff, a HS and College Referee, asks:

An attacker is NOT in an offside position when the ball is touched/kicked towards the goal by his teammate. He runs to an offside position before the ball arrives. Is it an offside foul?

Answer

We recommend that you use the search feature on the website and look for recent Q&As under the search category  “Law 11” – what you find there (this answer will also show up) can provide considerably more detail than what follows.

No.

OK, maybe a little more detail.  Your terminology is incorrect – and incorrect in a way that makes explaining the answer a bit more difficult.  So, let’s start simply with the incorrect terminology.  You say that this attacker was not in an offside position when a teammate last touched/played the ball.  Fine so far.  Then you say that “He runs to an offside position before the ball arrives.”  That is your downfall because, wherever that attacker was when he and the ball finally “connect,” he was not in an offside position.

“Offside” position is not a place on the field, it is a condition an attacker acquires by being in a certain place (ahead of the second-to-last defender, ahead of the ball, and ahead of the midfield line) at a certain time (the moment a teammate touches/plays the ball).  This “offside/onside” condition remains unchanged during whatever happens afterward until that “play” is over.  In short, if the attacker was not in an offside position when his teammate kicked the ball, then he can never thereafter be in an offside position no matter where the ball moves, no matter where he moves, no matter where his teammates move, and no matter where any of the defenders move … as long as it is the same play.

How do you know when it stops being the “same play”?  When (a) the ball leaves the field, (b) the referee stops play for any reason, (c) there is a new touch/play of the ball by a teammate, or (d) a defender clearly gains possession and control of the ball (except for a “deliberate save”).  In the case of (c), a new determination for all attackers must be made as to their individual offside/onside positions.  In (d), determinations must also be made as to offside/onside positions but, this time, it’s the opposing team players who have to be evaluated because, guess what, they are now the attackers!

Since, according to the scenario you provided, the attacker wasn’t in an offside position when he made contact with the ball (because he wasn’t in an offside position when the play began), then by definition he did not commit any offside offense when he himself touched/played the ball.  We call this “coming from an onside position” and it is one of the most misunderstood aspects of Law 11 because everyone else (excepting the officiating team, of course) thinks in terms of where everyone is when the play ends, whereas we as officials have to pay attention to where everyone was when the play began.  The evil twin to “coming from an onside position” is “coming from an offside position” — it is equally misunderstood but we’ll leave that for some other Q&A.

Oh, and by the way, one other item of incorrect terminology … offside is not a foul.  It is an “offense” — only an offense covered in the first part of Law 12 can be termed a “foul.”

CLOSURE on Notice, Apology, and Regrets

A Note to Readers of this website:

When this message first appeared, it was very long and laid out our newest challenge involving a total shutdown of the website, making it inaccessible, and the loss of all previously posted Q&As since mid-May and all Challenge questions since the posting of #2.  Subsequently, the message was revised to  announce that, by very good luck (with maybe a bit of clean living thrown in), our awesome webmaster had recovered some of the lost material and one of our readers could supply what was still missing because he kept a personal copy of the posts.

Today, we are very happy to announce that all the recovered material has been transferred to the site.  The posts that our webmaster discovered are now chronologically where they were originally while the rest of the posts were converted and reposted currently with a note as to when they had appeared originally.  Prior Challenge Questions 2 – 4 (with their answers) and current Challenge Question #5 have been added back to the Challenge tab.  #5 will be closed out sometime in early December and #6 will be offered for consideration.

We sincerely hope that this event, added to the earlier server problem which refused to pass along to us nearly two months of questions (whose eventually posted answers, ironically, were among those also lost in this latest event), marks the end of our troubles for a while.   We are now fully back in business.

A Clarification Unrelated to Any Question

(Originally published on 10/22/17, “Operation Restore”)

From time to time, we become aware of an authoritative clarification of some element in the Laws of the Game and it is our intention to make sure that this website’s readers are informed.  This posting relates to a relatively brief, somewhat unexpected, and a bit confusing new sentence that was added in 2016 to Law 12 immediately following the list of those seven actions (a.k.a. fouls) for which a direct free kick should be the response if the action were careless or reckless or performed with excessive force.  Here is the sentence (p. 82 in 2016, p. 95 in 2017):

If an offence involves contact it is penalised by a direct free kick or penalty kick.

Among the seven offenses in the list prior to the above sentence were three which explicitly included the attempt to perform the action (striking, kicking, or tripping).  Attempting to do something like striking, kicking, or tripping normally implies that, being unsuccessful, the action missed — i.e., did not involve contact.  Adding a bit of mystery to this issue was the introduction into the 2016 edition of the Laws of the Game (continued in this year’s edition) of the first specific and concrete distinction between impeding involving contact and impeding not involving contact with the added admonition that the latter was an indirect free kick foul while the former, because of the contact, must be considered a direct free kick (or penalty kick) offense.

The explanation in 2016 did not clarify the reason or purpose of this sentence and was primarily a simple restatement of its language.  It has now been clarified.  We thought that the positioning of the new sentence was unusual (right in the middle of Law content related to direct free kick offenses).  It turns out that the reason the sentence was added was because a disturbing number of Referees (no numbers, no indication of where they were, etc.) were treating a “dangerous play” event involving the so-called “high kick” as still an indirect free kick offense even if the kick was not only high but also made contact with the opponent!  To disabuse Referees of this notion, the sentence was intended to advise all Referees that an indirect free kick offense can become a direct free kick offense if it includes contact with an opponent.

This was abundantly clear given the International Board’s Law revisions involving impeding (with and without contact) but, for some reason, the Board handled the application of this concept differently in the case of dangerous play.  We personally felt that that the principle the Board was setting forth here (an eminently reasonable one which has been part of USSF training for years, we should add) might have been more clearly understood if the sentence had, for example, been located in the section on IFK offenses or if each of the IFK offenses that might involve physical contact with an opponent could have been rewritten (as the Board did with impeding) to emphasize that an IFK foul which included physical contact raised the level of the offense to that of the DFK/PK offense.

Impeding (of course) and now dangerous play have this contact/no contact distinction but the principle could just as well be extended to interfering with the goalkeeper’s release of the ball into play.  It seems to us reasonable, for example, to treat kicking the ball out of the goalkeeper’s hand(s) as a DFK offense since a ball in the goalkeeper’s possession is an extension of the goalkeeper and therefore kicking a ball held by the goalkeeper is the functional equivalent of kicking the goalkeeper — ergo, a DFK restart (with possible misconduct punishment levied the same way as would be considered appropriate if the kick had been delivered directly to the goalkeeper’s body).  This also, by the way, has been the guideline used in USSF Referee training for more than 20 years.

Ending A Period of Play

Maninder, a HS/College fan, asks:

Today in a match ( Real Madrid vs Malaga), it was first half injury time going on, i.e in the 47th minute. Malaga got a free kick.  The Malaga player kicks the ball into Real Madrid’s penalty area and another Malaga player scored from a header.  But the goal wasn’t given because the Referee blew the halftime whistle just after the Malaga player kicks the ball.  Is this the right thing from the Referee?

Answer

There is no kind way to answer this because the correct answer is absolutely clear – yes.  Maybe.  Probably.  Hopefully.  We, of course, have no way of knowing what was in the Referee’s mind when he whistled.  Ironically, the questioner above is a HS/College fan where none of what follows is a serious problem because HS and College matches in the US use a visible stadium clock, officially stop/start time for various things during a period of play, and sound a loud horn to stop play when the count-down reaches 0!  In the match cited in the question and all other matches played under the Laws of the Game, time is controlled solely by the Referee.

The point is that the Law is very inarguable about match timing.  Assuming the half is 45 minutes, then the whistle blows to end play when the moment the watch count-up timer hits 45 (remembering that a 45 showing on the timer means that the 45th minute has ended, not begun). The  only exception is that a penalty kick signaled before the end of the 45th minute must  be taken regardless of the time, and the period ends when the PK ends.

But what about what is variably called “Referee time,” “injury time,” or “wasted time”?  The Referee must announce any additional time to the lowest full minute (i.e., 1 minute and 45 seconds is 1 minute, 45 seconds is 0 minutes, etc.) before the period of play is due to end.  When 45 minutes + that time is up, time is over and play must stop, no matter what is going on (unless, during this “extra” time there is further time wasted).  No flexibility in this element of the Law is allowed.  Stopping the half can happen just before a goal is scored or while play is stopped for a throw-in, goal kick, corner kick, etc.  Play can stop just before a player on your team is getting ready to make the game-winning shot on goal that will make them the champions (Boooo! Idiot Ref!) or the opposing team is getting ready to make the game-tying shot on goal that keeps your team from winning (Hurrah!  What a great Ref!).

There are some Referees who won’t stop play even if time is over if one team is attacking the opposing team’s goal from nearby.  They are wrong.  There are some Referees who would refuse to stop play even though time was up until a corner kick is completed (because they might score).  They are wrong.  There are Referees who, in a 9-0 game, might allow the team with no goals that just happens to look like they might score and he wants to give them a chance to go home with at least something.  They are wrong.  There are Referees who believe that the Law requires there to be a restart after every stoppage even if time ran out during the stoppage.  Except for a penalty kick, they are wrong.  There are some Referees who really hadn’t been keeping track of wasted time and thus hit the 44:50th minute with no notion of how much wasted time there had been but with the vague feeling that there had to have been some so they let play continue for a bit longer.  They are wrong.  Finally, there are Referees who know all time is up (both regulation and extra time) but they let play continue because they fear becoming the object of anger by one team or the other based on whatever was going on at the time.  They would be not only simply wrong but sadly wrong.

By the way, we have dealt before with questions regarding match timing and this is as good a place as any to draw every reader’s attention to the readily available “Search” feature ( try the “Law 7 – Duration” category).  We decided to answer this question even though it (or something like it) has already been asked and answered because we felt this building up inside and needed to get it out.  We feel much better now, thanks.  And, getting back to the Referee, he was entirely within the Law if (a) the match was set at 45 minutes for each half (as usual), (b) he announced before the 45th minute that there were 2 minutes of additional time, and (c) there was no excessive loss of time during the extra 2 minutes.

The Plight of Goalkeepers

(Originally published on 10/17/17, “Operation Restore”)

Kaleb, a U13 – U19 player, asks:

Yesterday during my soccer game I was playing goalie.  I stopped the ball and started to get up so I could kick the ball up the field.  A person from the other team started running full force at me (note, I still had the ball in my hands) so I snapped one arm out in front of my body and the person from the other team hit my arm. The Referee immediately called a penalty on me for using my arm as a weapon.  I didn’t swing my arm at him I just put my arm up to protect myself and he hit my arm.  I would like to know if putting your arm up to defend yourself is a penalty.

Answer

Could be.  This is one of those judgment calls for which “you had to be there” in order to get some sense of what the Referee saw — the decision depends on so many variables.  We will say that, in general, the picture we get when you said that you “snapped one arm out in front of my body” is the classic football (American football) photo of a pigskin carrier running down field with an arm held out to fend off opponents trying to stop him.

Let’s just admit up front that the job of a goalkeeper is, as one observer noted, marked by “80 minutes of boredom and 10 minutes of terror.”  In other words, it’s not easy and every goalkeeper walks a thin line in situations like this between trying to stay uninjured and doing their job, a job which often requires the goalkeeper to get into positions on the ground or in the air which are inherently risky.  Having had some experience with serving in this position, we also understand that some goalkeepers take advantage of the quick, brief dust-ups that are a normal part of the goalkeeper’s life to respond in ways that are, shall we say, unforgiving of opponents.  Opponents, on the other hand, generally are not very forgiving of goalkeepers (except their own, of course) when it comes to a willingness to take their efforts to continue attacking the goal right to, and sometimes beyond, the edge of the goalkeeper’s safety.

All that said, it is the job of the Referee in situations involving challenges to or in the vicinity of the opposing goalkeeper to remember that the Laws of the Gamer require such challenges to cease immediately once the goalkeeper has control of the ball. “Control of the ball” is marked generally by having both hands on the ball or one hand on the ball against any kind of surface (ground, body, goalpost, etc.).  Keeping in mind the need to factor in the age, skill, and experience of the players, Referees should be proactive in safeguarding the goalkeeper where the flow of play appears to include one or more opponents acting recklessly despite the goalkeeper arguably having control of the ball.  In your scenario, the Referee should have begun closely monitoring the actions of the opponent who had “started running full force” at you, repositioning to warn the opponent that his behavior was being observed, and even providing a strong verbal caution against violating the Law, all in an attempt to forestall the impending offense.  At some point, the apparent intent to interfere by the opponent would warrant a preemptive whistle.

On the other hand, you are not warranted in taking actions which go beyond mere “self protection” — after all, a more effective way to protect yourself in a case like this would be to simply sidestep the onrushing opponent.  This often does not appeal to more macho goalkeepers whose mindset is, “it’s his job to avoid me so I will simply stand my ground and maybe get in a bit of mayhem on my own which will probably be ignored or justified by the Referee.”

In short, while we would have preferred to see the Referee in this case act in advance to prevent or stop a rapidly building momentum which, if left unchecked, is only likely to end badly for everyone involved in the likely collision, you had other opportunities besides snapping your arm outward in what could only be termed an aggressive manner.  Hence our answer at the beginning of all this — yes, it could be a penalty (i.e., determined to be “striking” and, since it was by a defender within his own penalty area, leading to a penalty kick restart).

Better for all concerned, however, would have been a whistle by the Referee to stop play as the opponent’s run brought him close enough to justify a decision that there was an intent to interfere with the release of the ball into play, resulting in a caution for the opponent for unsporting behavior and an IFK restart for the defending team.  Better yet would have been proactive officiating aimed at getting it through the opponent’s head that he needed to stop running at the goalkeeper once control of the ball was established.

 

Advantage vs. Offside Offense

(Originally published on 10/4/17, “Operation Restore”)

ST, an adult amateur referee, asks:

An attacker is fouled by a late tackle by a defender after the ball was passed to his teammate (foul was not cardable).  The Referee saw the teammate was in good attacking position so he shouted advantage and gave the signal.  What the referee didn’t know was the teammate was in an offside position so, when he received the ball, the AR flagged to signal an offside offense. Should the referee blow the whistle and give a DFK to the attacking team?

Answer

Yes.

To understand why, we have to explore the intersection of advantage decisions and off side offenses.  Law 5 makes it clear that an advantage decision, once given, can be called back if the advantage that was originally thought to exist does not materialize or could not be maintained over the course of the next several seconds.  This normally is the result of such developments as the ball possession being lost or the fouled player being unable to maintain his equilibrium.

Note #1: advantage is a team concept  and applies potentially to the attacker’s entire team so the issue is not always what happens to the fouled attacker but what happens to the attacking team’s overall ability to maintain a credible attack against the opponents.

Note #2: we did not say whether they might be able to score a goal — that gets into “obvious goal scoring opportunity” (OGSO) which, though similar, is a different issue.  The key phrase for advantage is the ability to maintain a credible attack moving forward.  And this, in turn, leads us to include scenarios in which the attacker, though fouled and as a result losing his personal control of the ball, is nevertheless able to get the ball to one or more other members of his team.  All of this must be taken into consideration after the Referee has signaled for advantage.  If this credible attack cannot be kept going forward either by the fouled attacker or by the attacker’s team, Law 5 requires that we stop play and return to the original foul.

Note #3: the Laws of the Game seriously frown on using advantage if the offense involves violence of any kind.  That was not the case here because, as the scenario states, the original foul was not cardable.  If it had been an offense which would draw a red card for SFP or VC or Spitting, stop play and deal with it.

What happened in the given scenario?  Everything looks fine, up to a point.  The foul (late tackle) was called (yes, it was because the advantage signal is a declaration that the foul occurred).  For the next few seconds, we are going to see what happens.  If the attack remains credible, we let that foul go (but come back at the next stoppage if there was any nonviolent misconduct); if it does not, we come back to the original foul.

Here, the Referee judged that the team would be able to maintain its attack if the ball released by the fouled attacker went to his teammate.  Remember, at this time the teammate who was the intended recipient of the pass and who was objectively in an offside position had not yet committed any offense.  For whatever reason, the Referee failed to “read” the offside position status of this teammate but, even so, while we might quibble about whether the Referee should have foreseen the problem, there remained in the several seconds of the “advantage time” the possibility that another teammate might come roaring out of nowhere and control the ball before it even got to the intended recipient — in which case, everything could have proceeded as expected.

That did not happen, the intended recipient in an offside position made the mistake of interfering with play while in that position, an offense which would otherwise have resulted in control of the ball simply passing to the opposing team for an IFK restart but for the fact that the game was “sitting on” advantage time.  Because it was, the Referee should come back to the original foul and restart with a DFK where the foul occurred.  If questioned, the Referee need only reply (if a response were needed) that “the advantage did not materialize.”  Look at it this way.  What the Law did was to say that the teammate in the offside position was, for all practical purposes, not there and could not play the ball anyway.  It was the functional equivalent of having desperately played the ball into space with no chance that anyone on his team would get it (in which case, the return to the original foul would be obvious).  The fact that the teammate did touch the ball is irrelevant because the real issue is that, following a foul, the fouled player’s team could not continue to make a credible attack forward.  This result would have been the same if the teammate, realizing his offside position, simply stepped aside without making contact with the ball.

 

 

Straightforward Offside

(Originally published on 7/30/17, “Operation Restore”)

Jim, a U13 – U19 coach, asks:

A player is on a breakaway and scores with a clean shot past the goalie. The goalie makes an aggressive tackle and injures the player on the play inside the 18 yard line. The goal is subsequently called off because of an offside violation.  Obviously the goal is not allowed, but what is the correct call in relation to the dangerous tackle on the now injured player?

Answer

We are going to treat this as  a straightforward sequence of play and not delve into any of the possible complications, interesting though some of them might be.  Accordingly, our answer is based on the following: attacker makes a shot on goal which goes into the net, then the defending goalkeeper aggressively tackles the opponent and injures him, then the decision is announced that the goal is not allowed based on the attacker having committed an offside violation.

Where several offenses occur sequentially (i.e., one after another), the first offense determines the restart.  Here, the first offense was an offside violation so the punishment is an indirect free kick taken from where the attacker became involved in active play by touching the ball (which subsequently went into the net so the apparent goal has to be canceled).

The second offense was a tackle which, by its description, would seem to meet the definition of having been taken with excessive force and without regard for the safety of the opponent. However, because play was already considered to have been stopped when the offside offense was committed, the goalkeeper’s action was not a foul but it is misconduct.  The goalkeeper should be sent off and shown the red card for violent conduct.

Just as an indication of how and where this could become sticky, the offside offense and the excessive force tackle could have happened at the same time — we would not like to try to figure that one out.  Most referees would probably avoid the problem by declaring the events were sequential rather than simultaneous.

 

 

Backpass and Advantage

(Originally published on 7/22/17, “Operation Restore”)

Wilson, an adult amateur parent, asks:

On a game I watched today the defender made a pass to the keeper but the ball was heading to goal.  The keeper then decided to deflect the ball with her hands.  She touched the ball but could not hold it.  The ball kept going towards goal, the attacker kicked it in and scored.  The Referee disallowed the goal and gave the attacking team an indirect kick for the backpass.  Shouldn’t the Referee have applied advantage, since calling the backpass benefited the offending team?

Answer

Good heavens, why would the Referee not have applied advantage?  Except for someone very inexperienced, whose mind was still fixated on “call the foul,” Referees past their fifth or sixth season should be positively looking for opportunities to demonstrate that they know how the game is played by waiting a moment to see what happens next and only then deciding what to do.  Pavlovian reactions to fouls cause more trouble in games with experienced players than almost anything else we can think of (excepting total ineptitude).

The “pass back to the goalkeeper” offense (the very term is misleading — it doesn’t have to be back, it doesn’t have to be a pass, and it doesn’t have to be to the goalkeeper) is an offense like any other and there is no reason to think it is exempt from the use of advantage.  We find utterly mysterious how the Referee could have thought this was a good decision since it replaced a 100% goal with  (given that the restart was an indirect free kick facing what was probably an impenetrable wall) a 20% goal at best.

We are getting uptight and perturbed discussing this so we had better stop.  The answer is, Yes.

 

Injured Referee

(Originally published on 7/21/17, “Operation Restore”)

Murray, an adult amateur fan, asks:

If a Referee gets injured and there is no replacement, does the result at the time stand or does it depend on the time the game was stopped?

Answer

Yes, if the Referee is the only official assigned to and present at the match.  Yes, if there are other officials but none is qualified to take the Referee position and responsibilities.  No, if there is at least one other member of the assigned officiating team qualified and willing to take the Referee position.

In matches with a full crew assigned (Referee and two Assistant Referees), one of the Assistant Referees is often designated as AR-1 and this is usually for the purpose of identifying that AR as the official who takes over if the Referee is unable to continue (in which case a volunteer linesman could be sought for the AR-1’s position) or is unable to serve as the Referee but deemed able to swap places with the AR for the remainder of the match.  Alternately, the local rules of competition may specify another method.  If no method is specified and there is no prior designation of one of the ARs as “senior” or first in line to take over, the Referee would usually be expected to designate which AR (assuming that AR is amenable) would take over the Referee’s position.

Are you getting the feeling the assumption is that Referees are not expected to become sufficiently unable to continue to the point of needing a replacement?  You would be correct.  If you are not comfortable with that ambiguity, ask the Assignor or know in advance if there are any rules in place or traditional in your area which govern this sort of problem.

If none of these options is available or acceptable or workable, the match is terminated, after which the resolution of your question is in the hands of the local competition authority (the body under whose authority the particular game is being played).  In any event, full details must be included in the match report.