The extra training may have caused the bursa under the tip of the scapula to become inflamed. This condition is called scapulothoracic bursitis. A bursa is a lubricated sac that helps decrease friction between tendons and muscles when they move. The repeated arm motions of baseball pitching can irritate the bursa underneath the scapula. It becomes inflamed and painful. It also begins to pop during the windup, as the arm is cocked back and gains speed for the throw. The first method of treatment is to rest your sore shoulder. Talk to the team doctor or a family physician for other suggestions.