Replying to My knee grew a ballsack...

So I fell on my knees on concrete the other day (playing an epic game of ninja at school). They hurt like motherfuckers, but I realized that my right knee felt tight in my pants not too long afterward. When I checked it out, my knee looked like it had a sack that was nurturing a fucking baby kangaroo. It was filled with some weird liquid and at some points I could almost push an entire centimeter of swishiness before touching bone. Has this happened to anyone? I'm not sure if its a hematoma filled with blood, or something else. Tomorrow and after tomorrow are the last 2 days of my season and one sack bouncing around is already enough for me. Any ideas? Key discussion words: Knee, ballsack, kangaroo, jiggle, urine in rectum...Go!