Same thing happened to me not that long ago.. I was playing a fun friendly game against inferior competition. So I think my body wasn't in "sports mode" kinda like in warmups took of for a dunk and yeah... Worst thing is that you put more force into that step than usual because you're about to jump... Also had a grade 2 sprain. I'm 6'6 don't want to imagine how much worse it would have been if I was 7 foot tall