José Mourinho was quite right in questioning referee Michael Oliver’s decision to dish out a second yellow card to Ander Herrera in the 35th minute. He had, after all, let almost all other incidents go without a caution, and would let most other incidents go without one the rest of the way as well. Despite the rather noticeable amount of fouls committed by United (14 were called), they collected only three yellow cards, and the only other player booked besides Ander Herrera was Ashley Young. How Marcos Rojo and Phil Jones, for example, escaped without a card is beyond me.

Of the 14 called fouls, no less than 6 were committed against Eden Hazard. United’s gameplan was quite clear, with Mourinho resorting to hack-a-Hazard like so many other teams tried back when we still believed in the Second Mourinho Dynasty. While I don’t have exact individual numbers, United committed 8 fouls in the first 35 minutes, until the sending off, then wouldn’t commit another one until the 75th. The strategy was clear, the target obvious.

Fortunately for Chelsea, Michael Oliver decided to do something about it. It possibly could’ve been handled differently (a yellow for, say, Jones for one of his obvious yellow card-worthy fouls could have changed the flow of the game), but this way we get to talk about what “persistent fouling” means and how to apply it.

As is their habit, FIFA’s Laws of the Game (and the associated guidelines) are maddeningly vague and leave lots of room for interpretation, judgement, and what they hope is common sense. For example, Law 12 simply states, under cautionable offenses: “persistent infringement of the Laws of the Game (no specific number or pattern of infringements constitutes “persistent”)”.

In their official guidelines, FIFA expand a bit on Law 12 to help interpret it for application. The relevant part about persistent infringement reads:

Referees should be alert at all times to players who persistently infringe the Laws. In particular, they must be aware that, even if a player commits a number of different offences, he must still be cautioned for persistently infringing the Laws. It is generally advisable, though not required, to warn a player that he is nearing the threshold level before actually applying the sanction of a caution. There is no specific number of infringements which constitutes “persistence” or the presence of a pattern — this is entirely a matter of judgement and must be determined in the context of effective game management. Referees should consider the following circumstances:

1. The length of time during which the fouls occur — spread out over 90 minutes of play may not be as serious as the same number committed over the space near of 15 minutes

2. The fouls themselves can be of various types (generally, those described in Law 12 but including as well repeated violations of Law 14)

3. Fouls to which advantage has been applied must be included in determining “persistence”

The obvious definition of persistent fouling is a defender committing multiple small fouls throughout the game (on various targets), and after (usually) receiving a warning, eventually getting booked. Think Ramires or even Oscar, or most of the best defensive midfielders. It is under this interpretation that the second Ander Herrera yellow looks harsh.

But the key passage of play was Oliver giving both Jones and United captain Chris Smalling a talking to just seconds prior, after yet another foul on Hazard. Oliver quite clearly figured out the gameplan and presumably called Smalling over to let him know, as the captain, that his team needed to stop with the constant fouls on Hazard or the yellows were going to start dropping.

Not 30 seconds later, Ander Herrera upends Hazard from behind, his challenge nowhere near the ball. Oliver did not hesitate for a second.

Soon, enterprising Twitterers and Redditors found a relevant guideline to help explain the referee’s thinking — though it should be noted that in the clip above, the former Arsenal and West Ham midfielder Stewart Robson, who was doing the color commentary alongside Martin Tyler, caught on quite quickly to what was happening as well, leading me to believe that this is not entirely a foreign concept to football players.

The guideline comes from the US Soccer Federation’s “Advice to Referees”, which is an official publication to help interpret FIFA’s rules. While these obviously aren’t FA or PGMOL publications, the laws of the game and the guidelines for applying the laws of the game should be universal. (That’s part of the mandate of FIFA!)

So, the USSF’s advice goes, in part (on page 55 in this PDF version):

12.28.3 PERSISTENT INFRINGEMENT

Persistent infringement occurs when a player repeatedly commits fouls or certain other infringements. It is not necessary for the multiple fouls to be of the same type or all to be direct free kick fouls, but infringements must be among those covered in Law 12 or involve repeated violations of Law 14. In most cases, the referee should warn the player that the pattern has been observed and, upon a subsequent violation, must then issue the caution. If the pattern is quickly and blatantly established, then the warning should be omitted and the referee should take immediate action. In determining whether there is persistent infringement, all fouls are considered, including those to which advantage has been applied.

So that’s the interpretation we commonly operate under. Repeated fouls committed by one player, who is then cautioned at the referee’s discretion.

But here’s is where the advice gets interesting.

The referee must also recognize when a single opponent has become the target of fouls by multiple players. As above, upon recognizing the pattern, the referee should clearly indicate that the pattern has been observed and that further fouls against this opponent must cease. If another player commits a foul against the targeted opponent, that player must be cautioned but, in this case, the misconduct should be reported as unsporting behavior, as must any subsequent caution of any further foul against that same targeted opponent. Eventually, the team will get the message.

If this advice were in a textbook, they’d illustrate it with the first 35 minutes of the Monday’s match. Oliver warned the team that he recognized the pattern of fouling and cautioned the very next player who took out the targeted opponent. Unfortunately for Mourinho’s side, the player committing the foul already happened to be booked. To his credit, Oliver followed through on his threat/promise.

His decisions may not have been approved by most, but at least he was consistent in not dishing out yellow cards and following through in the one instance he actually drew a line in the sand.