I think it depends on a) your tone of voice and b) what it is that you're yelling. If it's just a bit of encouragement, for example 'Yeah, well done, you're going great etc.. ' that's one thing, but sometimes telling your kids what to do eg. 'Try harder, throw it further, get in there,' etc can have a very discouraging effect. It's also important that your remarks are not disparaging to your child, or to other players and coaches. I would leave the coaching to the coach during games, and perhaps save your input for when you are just playing with him on your own? I have a son who is probably around your son's age and most parents I know would agree that winning/losing, even your child's skill level is not as important as your son being part of a team. You need to let your son's coach do his job. I think the parent's job at sporting events is just to be a supportive and encouraging parent - not just to your own child, but to all the children playing.