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.
Fatwa of Shaykh Ibn ‘Uthaymeen from Fataawa Islamiyyah, vol. 4, p. 430