Ruling on wearing shorts when playing sport and exercising

Playing sport is permissible if that does not distract one
from something that is obligatory. If it distracts you from something that
is obligatory then it becomes haraam, and if it becomes a person’s way of
life so that it takes up most of his time, then it is a waste of time, and
in this case at the very least it is makrooh.

 With regard to playing sport wearing only shorts which show
the thighs or most of them, this is not permissible. The correct view is
that young men must cover their thighs, and it is not permissible to watch
players when they have their thighs uncovered in this manner.