My daughter also does this. She does not do it in public but I catch her doing it in her room alot. She says she does not know why she does it. I am confused on why she is doing these things....HELP
If he is medically ok, then it may be that he just likes to fidget and has unfortunately gotten stuck on this one. Like how some people bite their nails, they are hardly aware they are doing it. You will need to find him something else to do with his hands. An interesting textured keyring on his beltloop to finger, for example.
You definitely should have him examined, in the event that he is trying to alleviate some discomfort. From a behavior management perspective, the wearing of a belt (it needn't be confined to jeans) might be helpful because to some extent it interrupts the behavior. However, as you've seen at baseball, it doesn't stop the behavior. If he is OK on the medical front, and the behavior has developed into a habit whereby he soothes himself, be straightforward in setting limits on it. Don't be shy to talk with him about the inappropriateness of this behavior in a public setting. Help him to see that it is perfectly OK in a private setting. Some children who are unusually insecure or anxious do this, and if that is the case it would make sense to seek an evaluation with a perdiatric mental health clinician.