What the rotator cuff is
The rotator cuff is located in the shoulder and consists of four muscles and their attached tendons. These muscles are the supraspinatus, infraspinatus, teres minor, and subscapularis. Together, they form a protective sleeve around the shoulder joint. The rotator cuff keeps the upper arm bone firmly in its socket while allowing a wide range of motion. Without these muscles, the shoulder would be unstable and unable to function properly.
Why it matters in baseball
Baseball pitchers put enormous stress on their rotator cuff muscles when throwing. A typical pitch involves rapid acceleration and deceleration of the arm, which requires the rotator cuff to generate force and then control the arm's movement. The rotator cuff muscles must fire in precise sequence to produce a fast, accurate throw. Because pitchers throw repeatedly during games and practice, their rotator cuff muscles are under constant demand and at high risk of injury.
Common rotator cuff injuries
Pitchers frequently experience rotator cuff strains, tendinitis, and tears. Strains occur when the muscles are stretched too far or too forcefully. Tendinitis is inflammation of the tendons from overuse. Tears happen when the tissue is damaged or ruptured, which can range from partial to complete. These injuries develop gradually over time from repeated throwing or suddenly from a single forceful throw. Pain, weakness, and limited shoulder movement are typical symptoms.
Prevention and treatment
Pitchers can reduce rotator cuff injuries through proper warm-up exercises, strength training, and correct throwing technique. Rest days between games allow muscles to recover and repair. Coaches monitor pitch counts to prevent overuse in young players. When injuries occur, treatment ranges from rest and physical therapy for minor strains to surgery for severe tears. Recovery time varies greatly depending on the severity of the injury. 
Answer