Classic baseball confrontations are decidedly physical, all-or-nothing encounters in an otherwise non-contact sport. The forces generated by player-on-player collisions can be significant, creating a risk of serious injury. Knee and lower leg injuries and concussions are common occurrences when two players collide at home plate.
However, while most baseball injuries are far less dramatic than those occurring at home plate, they are often as debilitating in the longer term. Baseball has historically placed significant emphasis on training programs that stress the repetition of various physical movements, in the development of throwing, hitting, and base-running skills. The sport has a correspondingly very high incidence of injuries resulting from an overload on the ability of a structure to endure the repetitive movement, particularly arms and shoulders. The structural overload is made worse in players that employ poor mechanics in their execution of a particular baseball fundamental, which accelerates the breakdown of the joint or structure in question.
The over-hand throwing of a baseball by a pitcher is an unnatural motion for the elbow and the shoulder to endure. For this reason, pitchers sustain more injuries than any other baseball player. By contrast, the underarm motion employed by a softball pitcher places a low degree of strain on these structures; it is not uncommon for softball pitchers to be active well into their 40s.
The mechanism of the baseball pitch involves rotation of the shoulder joint, twisting of the upper arm and elbow, extension of the forearm, and flexion of the wrist.
All of these actions are performed at a high speed, placing considerable stress on every part of the arm. In a typical high-level amateur or professional game, a pitcher may throw 100 pitches or more in the game itself, with as a many or more pitches as part of a warm up. The stress placed upon a pitcher's arm does not begin when the player reaches the upper echelons of competition; the nature of baseball is such that pitchers are groomed at young ages, and the physical problems that they encounter as adult athletes often have their roots in the player's activities as a youth. A study conducted by the American Sports Medicine Institute determined that approximately 58% of pitchers under the age of 18 sustained a significant elbow injury either during or after competition.
It is believed that the most physically difficult baseball pitch to throw, the curveball, is the primary cause of both elbow and shoulder injuries in pitchers. The curveball requires both the pitching shoulder and elbow to be rotated as the ball is being delivered so as to impart spin on the ball that will cause it to dip, or curve.
Elbow injuries occurring in baseball have three separate causes. The first and most devastating is an injury to the medial aspect of the elbow, the ulnar collateral ligament (UCL). As the pitcher delivers the ball, it is raised behind and above the shoulder. A significant force is then generated as the arm moves past the ear and rotates, and the UCL pulls the forearm of the throwing arm forward. As the UCL is a small structure that, as the ball is pitched, is subjected to the entire force of the arm's movement, this force can cause the UCL to sustain a micro tear. In typical circumstances of muscle or ligature strengthening in the body, a micro tear is a part of the building and strengthening process. With the constant exposure to this force that occurs in baseball pitching, the UCL micro tear will often progress to a larger, more complete and disabling tear.
The second common elbow injury sustained by pitchers is when the radius (arm bone) is brought into contact with the humerus (forearm bone) in the joint, resulting in bone chips that may move within the joint, causing pain.
The third common elbow injury is created by the straightening of the elbow on the delivery of the ball at the point where the ball is released, which through repetition causes the elbow components to grind together. This also may result in bone chips in the joint, which can disable the pitcher.
Each of these injuries will usually require surgery, and an extensive period of rehabilitation. The surgery perfected by Dr. Frank Jobe, whose most prominent patient was major league pitcher Tommy John, involves the grafting of a transplanted ligament to the damaged UCL. This procedure has extended the career of numerous injured major league pitchers.
The serious shoulder injuries sustained by pitchers primarily relate to the rotator cuff. The rotation of the shoulder during a pitching motion will often lead to a grinding or displacement of the structure. Another common injury is a tear of the upper part of the bicep muscle. All of these injuries have their foundation in poor mechanics that are employed for a number of baseball seasons and have a negative cumulative effect.
The swinging of the bat during a baseball game is rarely the cause of a serious injury. However, batters develop strained muscles in their arms and low back, the result of repetitive strain caused primarily in training. The explosive movement of swinging a baseball bat as hard as possible may cause a spontaneous tear or rupture of a muscle or ligament in the shoulders or back. Such occurrences are rare.
As with any sport where the athlete is stationary for large portions of competition, the requirement of sudden, explosive movement such as running can pace significant strains on the body. Groin strains, as well as muscle pulls in the quadriceps (thigh) and hamstrings, are a common result. Sliding to avoid the tag of the defensive player may also cause injury to the gluteal muscles (buttock) and legs. With the exception of plays when a base runner collides with another player, baseball running injuries are rarely serious.
Diving for a ball in the outfield, especially on harder artificial surfaces, may cause abrasions to the skin.
Whether it is the catcher being struck by the ball with a foul tip, the batter being struck by a pitch, or the pitcher facing a "come backer" from a batter's ball, a baseball has the potential to cause a serious injury. Both catchers and batters wear protective helmets. However, head injuries caused by a player being hit by a baseball almost always occur on line drives that strike a pitcher or infielder.