My legs really hurt, I can't even sit down without pain?

Today I was playing handball at school and then suddenly, as I bent my knees, a shooting pain went straight up both of my thighs, it even made me get goosebumps. I kept on playing handball, trying not to sit down because it really hurt. Then, in my other classes, when I sat down, it was really painful, I could barely bend my knees. Also when I went to stand up, they really hurt. When I was walking and once I had sat down, they didn't even hurt. I've tried massaging them, but they still hurt. What could have caused this and is there anything I could do to stop it?