We ALWAYS clap for both teams-- a good hit is a good hit. This is not the World Series. We ALWAYS say good game-- even when they lose by 20.
It is hard to sometimes keep quiet on the sidelines, depending on the level of direction the coach gives, but they say it's best to sit down and shut up ;) BUT, if your child is having BEHAVIORAL issues, you need to step in, especially if there's a potential for injury to themselves or other kids.
Overall, remember your spectator sportsmanship too!