If both rotator cuff tears and tennis elbow are pitcher's injuries, then injuries to the knee are most likely to happen to runners. An impact against the knee or a sudden twist of the joint, like the kind a baseball player makes while rounding the bases, can rip the cartilage in the meniscus and that means a lot of pain. Fortunately, meniscus injuries can heal over time, but really bad ones need some help from a surgeon.
Another way in which the knee can become injured is if the ligaments that hold the upper part of the leg to the lower leg become strained or torn. Like injuries to the meniscus, these injuries are caused by sudden changes in speed and direction while running -- and, gee, that's what baseball players are doing all the time!