Okay, yesterday i was playing a casual game of football with friends. I was running backwards and was knocked off balance causing me to lose my footing and fall. It felt as if I hyper extended my knee, it also sorta popped. I can not walk on it and it is swollen on the inside part of my knee cap. If I try to stand it kind of rolls and automatically buckles, almost wobbling on it. The pain is tollerable but still is painful. what did I do?