does running help make ur leg stronger whihc leads to higher velocity?

Sprints can translate into the explosive strength to throw with more velocity. Long distance running wont help velocity, and some people would argue that it hurts.

Try hillrunning for leg strength:

alternate, 1 session jog up and sprint down, next session do the opposite

Running distance wont neccessarily increase velocity. You will have better luck long tossing and a well thought out throwing program, however running distances will build up leg strength and core strength which will keep your arm healthier and and build up endurance for games, ala Roger Clemens.