Unless he hits himself repeatedly in the male reproductive area to get a speed boost or some other reason, I couldn't see this been a issue.

I mean think about it most men I know had bikes as children wouldn't that also constitute infertility. Neither will clothing that keeps his "stuff" close to his body. It is true it can lower it a small amount due to heat, but most will be fixed in a day or too no permanent damage.

Now if he is running with no support that is a difference story that can cause a lot of damage.