How come i produce a lot mucus when i play basketball? normal?

Mucus where?: Some mucus from the nasal passages may be normal, or if a lot it could be allergies or vasomotor rhinitis, which are inconvenient symptoms but rarely dangerous - try an otc antihistamine like Claritin for relief if you want. If you are coughing a lot or the mucus seems to be coming from deep in your chest, see your primary care doc to get checked for exercise-induced asthma.