What did i do to my Patellar Tendon?

Today during my baseball game i was stealing second and i looked back and saw that it was a foul ball so i slowed up to turn around and right before i got to the bag i felt a weird pain in my knee (same spot as the Patellar) as i started to go back i tried to jog but every time i went to take my first stride a sharp pain shot through my knee. I don't know whats wrong with it but it hurts to put pressure on it and also i can walk but if i try to run or even jog it hurts as well as if i turn it a certain way. By the way i have had problems with it in the past but never anyway near this severe. Can someone please tell me what is wrong, how can i heal it and how long will it take.