Ouch that sounds like a good reason to shave.
But I wonder if he is just thinking about the hair being gone and not about the possible drawbacks of shaving such as irritated or dry skin, possibility of shaving cuts, itchiness when it grows back in, ingrown hairs...and just the pain of maintaining it. On the other hand, if it is just the lower legs those things are less likely to be a problem.
What events is it bothering him on? My younger DS always wears gym pants (not stirrup just regular gym pants) at practice, even when it is hot. He just prefers them. Would wearing pants for practice help?