R.C.
Hi,
Of course this could be just a habit, which gentle reminders might improve. And I can see why it would seem he has great balance because he can run and jump. But there are some children and adults who have great moving balance, but difficulty with "static balance", that is balance when standing in place or when not moving quickly. So perhaps you could have him checked at your local public school for his ability to balance , forward and backward. These are standard assessments used for young children and the screening is free. If he does have difficulty with these other skills, there are exercises and therapies available to build up this type of balance and they are provided free by public school systems.