frustrating when it seems like this took place, and its not just frustrating to parents. I have a son who is hypercompetitive and hates to lose. He works very hard at his sports, and when he doesn't win its hard for him and often affects how he feels for the rest of the day. I'm fine with him losing and think its a good thing for everyone to learn how to lose and to do it gracefully. But it is harder to do it gracefully when you feel like someone has his finger on the scale and the scale was or is not fair from the beginning. And in youth sports where skill levels vary so greatly from player to player, a few good players can really swing the odds in favor of one team over others.
Whether there is anything you can or should do about it is another question. My guess is that many times we have suspicions about it, but rarely have solid evidence that it has happened. So maybe we usually just have to work hard and try to make our own teams more competitive like others have said.