Kids are enamored by the media attention, salaries and superstar status of professional athletes. Pros used to be stars on Sunday. It's become more important than almost every other occupation on the planet. This leaves kids in a position to have to distinguish between what they see and what they know to be right. The fan rioting at some of Europe's soccer matches are case in point.
Poor sportsmanship is another.
Unfortunately so do their parents. Some parents just take it a couple of steps further. Usually the parent's intentions are good. They want to see their kid succeed, be the best at their sport of choice. When that gets taken to an extreme the consequences can be high.