K.F.
I know this goes beyond sports and I really can't help you much, but does he watch baseball? I've recently started and have you seen the mistakes the Rangers/Cardinals are making and they are the top two teams this year? It really puts it into perspective! I have an 11 year old that plays baseball and although he doesn't get down about a missed ball/strike out, etc there are so many parents (me included) that yell at the kids (not overly bad, but upset that they could make such a mistake :). Watching the pros make mistakes has really opened my eyes! They/We are human and all make mistakes. He does need to understand what it does to his team though, one child can affect the entire game as you stated. Good luck, but it is most likely his personality that you are just going to have to work around.