What kind of behavior? The first set are comments or complaints about the referee's calls (or non-calls). "Didn't you see that?" is one comment.
Or, on the other side, when a player is whistled for a foul, the "What me?" reaction is more and more prevalent.
The second set--per the cartoon above--is a tendency to "take a fall" when gently nudged, in the hope the referee will call a foul against the other team and issue a free kick to the "aggrieved" party.
It used to be the case that you didn't see this stuff until the boys were a bit older. Now, the little boys have learned it.
Of course, these tactics work against the interests of the boys who use them, in that they stop playing while they engage in their demonstrations, while the other team just keeps playing--often in possession of the ball. But that lesson is often missed, especially when the coaches aid and abet the bad behavior in their own comments--or in their silence.
Meanwhile, in contrast, check out this bit of good-hearted sportsmanship from a 2011 Manchester United vs Everton match: