If the torn ligament in question is along the outside of the elbow, it's likely to be the ulnar collateral ligament (UCL). Injuries to this ligament are common in throwing athletes.
Thirty years ago, such an injury might have ended his playing days. Today there are several different ways to repair damage to the UCL. Reconstruction using a tendon graft from some other place in the body is a popular way to go about this.
Taking tissue from the patient eliminates the problems of graft rejection that can occur with donor tissue. In the case of the UCL, the surgeon may use one of the round tendons located elsewhere. For example, the palmaris tendon in the palm of the hand is suitable. Likewise, the gracilis tendon along the inside of the upper thigh works well.