Simple solution on the soccer field, classroom, or at home:
At the first sign of unwarranted or undesired behavior, address it, make it obvious to everyone, and penalize it if necessary. At the second sign, up the punishment. There is no excuse for a kid taking the back of a kid's leg out with no chance to get the ball and having two refs just say play on. Every kid on the field then says to themselves, "Guess we get to do that to everyone today." And, you spit in my face, you lose teeth. If I had known that the kid has spit in my defender's face in front of the ref, I would have pulled my kids off the field.
It is our job to be the role models, whether as refs, coaches, etc. Do your job.
