The Ulnar Collateral Ligament (UCL) is a key ligament located in the elbow joint. It connects the humerus (upper arm bone) to the ulna (one of the forearm bones) and provides stability during arm movements, especially when throwing. Injuries to the UCL are common in athletes, particularly in sports like baseball. A torn UCL can lead to pain and instability in the elbow, often requiring rehabilitation or surgical intervention, such as the Tommy John surgery, to restore function and strength.