Jorge Posada is having a tough season. The five-time all-star catcher for the New York Yankees is batting below .200. Earlier this month, he asked not to play in a game because Yankees Manager Joe Girardi dropped him to the last spot in the Yankees’ lineup. Posada thought he should be batting higher.

It’s an old story in sports. A star player such as Posada gets old (he is 39) or injured. The team replaces the aging star with a younger player. The older player, who thinks he’s still good, gets mad at his team.

Quarterback Brett Favre threw for more than 70,000 yards and 500 touchdowns in his long, record-breaking career. But in his last season for the Minnesota Vikings, Favre threw a lot more interceptions than touchdowns. Shaquille O’Neal was a great basketball player years ago, but now he can barely run up and down the court for the Boston Celtics.

Great professional athletes often don’t know when to quit. It must be hard to give up the money and glory that come from playing a sport so well.

Kids who play sports have to make similar decisions. They don’t play games on TV or have million-dollar contracts. But kids who dream of being soccer stars might decide to quit the travel team because they’re not getting much playing time and instead play for fun on a recreation league team. Or they might decide to quit their softball team so they have time to be in school plays or the school band.

Yankees all-star Jorge Posada didn’t like it when his manager dropped him to last in the batting lineup. (Gregory Shamus/GETTY IMAGES)

How can kids and their parents make these tough choices?

First, if you love a sport, don’t quit just because you didn’t make a team. Often, the best players at age 10 are not the best players in high school or beyond. Kids’ bodies and skills develop at different rates. A lot can happen between ages 10 and 16. So keep playing if you like playing.

But you might want to stop playing a sport, or to play it at a less serious level, if the sport stops being fun. After all, sports are supposed to be a joy, not a job.

Another sign that you might want to stop playing is when you are not getting any better at your sport, and (this may be the most important thing) you don’t care that you’re not getting better. Trying to improve is a big part of sports.

Finally, sports are important, but they are not the only activity for kids. Some kids like music or dance or scouts more than sports. I encourage kids to try sports and to stay physically active. But if you’ve tried sports and found they’re not for you, maybe it’s time to quit.

Like some pros should.

Fred Bowen is the author of 16 sports books for kids. His latest book is “Real Hoops.”