I think kids are motivated by pro sports. If a basketball player does a special dunk, kids try to copy it. If a pro player gets into a fight, kids are talking about it the next day in school. They're not talking about who won the game. It's okay as long as kids know where to stop.
Most kids do.
If you are playing your rival in a really important game, you're going to talk trash to mess up the other guy. Kids realize that going back and forth with each other during a game is just a way of getting fired up. It's all about intimidation. I think it's funny watching girls scream back and forth. I don't think parents have the right to yell about a call.