The father's letter, obtained by InfoTel News, explains that his son was only getting two shifts a game, and no longer felt like he was part of the team.
"I think in youth sports there is certainly a place for competitiveness and competition. But the question is, does that kick in at nine-years-old?" said John O'Sullivan, founder of the Changing the Game Project, a group working to make children's sports a more positive experience.
"If you are going to select a player to play for your team at that age, you are also making a commitment that if they show up to practice and work hard and they do their best, they are going to get enough minutes to make it enjoyable."
O'Sullivan posted the letter on his group's Facebook page, and said it received more comments and shares than many of his recent posts.
"The idea that you are going to pick a kid on your team and never let them play, that doesn't make any sense to me at all," said O'Sullivan. "They've been entrusted to develop not only better athletes, but better people."
O'Sullivan believes there's been a 'professionalization' of youth sports.
"[Watch] ESPN or you put on YouTube and all you see in younger and younger kids performing. You have Little League World Series and everyone says 'I want my 11-year-old to be on Sportscentre.'"
"It's not really a healthy thing. We've taken the youth needs and values and priorities out of sports and replaced them with adult needs, values and priorities," said O'Sullivan.
As a result, kids are walking away from sports, according to O'Sullivan.
"Some people say sports teaches character but I disagree with that. Great coaches in sports teach character by intentionally teaching it."
To hear the full interview with John O'Sullivan, listen to the audio labelled Short benchingSuggest a correction