Just tearing your ACL is rare, there is typically subsequent damage, which causes a lot of pain (Meniscus, spraining other ligaments, torn muscle, chipped bones, bone bruises). I tried to stand up after being helped off the court, and it felt like I was being stabbed in the knee with a giant syringe. After a couple days it was no probs, I did plenty of athletic stuff before finally getting surgery. YMMV