There has been debate about the overall health of the shoulder of an overhead athlete, specifically that of baseball players.  With repetitive motion of throwing, and the long seasons, with improper care, it appears that injury is inevitable.  Baseball requires extreme peak forces to be exerted on the shoulder synovial joint, increasing likelihood of injury. Fortunately, there are things an athlete can do to decrease these probabilities.
To start, the anatomy of the shoulder needs to be addressed.  As mentioned before, the shoulder is a synovial joint, meaning it is a fluid-filled joint cavity, with versatile mobility, unlike other joints, such as cartilaginous or fibrous joints.  As seen in Figure 2, the humerus, coracoid process, acromion, clavicle, and scapula are the bones comprising the shoulder.  The mobility of the shoulder comes from the glenoid fossa insertion with greater tubercle of the humerus.  Surrounding the bones are the coracohumeral ligament, inferior transverse scapular ligament, bicep tendon, capsular ligament, subscapularis tendon, and supraspinatus tendon.  Tendons are dense connective tissue, attaching bone to bone.  Surrounding these ligaments of the joint cavity is muscle; bicep and tricep brachialis, coracobrachialis, pectoralis major and minor, deltoid, trapezius, teres minor, rhomboid, latissimus dorsi, and serratus anterior.  What covers the muscle is called fascia.  Fascia is fibrous connective tissue that surrounds muscles, known as epimysium.
Stecco et al. (2016) found that fascia modalities implying manual massage as treatment observed an improvement in overall health.  Since fascia is the most superficial, in terms of shoulder complex, it is of the upmost importance for overhead athletes to preserve the integrity of the shoulder fascia.  Driveline Baseball found that there are extreme levels of peak force placed on the shoulder during external rotation and scapular tilt (throwing motion layback), reaching upwards of 40 pounds of force on the shoulder complex.

Figure 1:  Estimating force on shoulder complex as related to mass, velocity, and time.

Figure 2:  Anterior and interior cross section of labeled shoulder joint cavity (https://netterimages.com/images/vpv/000/000/004/4375-0550×0475.jpg).
Initial mobility of each individual must be addressed, due to unique individuality of each athlete.  Based on each individual, certain corrective exercises need to be incorporated, but there is also a component of soft tissue, or fascial, massage.  Al Dajah (2014) found that soft tissue mobilization and proprioceptive neuromuscular facilitation significantly increased range of motion in shoulder complex impingement.  Although not all athletes may be suffering from shoulder impingement, Cool et al. (2015) found that an increase in musculature mobility can prevent injury.  As a result, soft tissue manipulation may be beneficial in developing relative stiffness and stability.
Implementation of foam rolling as myofascial release has been seen to significantly increase overall range of motion prior to overhead athletes with glenohumeral internal rotation (Fairall, 2016).  This form of soft tissue manipulation is easily implemented and extremely beneficial for overhead athletes.

Figure 3:  Self-myofascial release with the use of a lacrosse ball on pectoralis major and minor, but can also be used posteriorly on muscle used for deceleration of a throwing motion (http://www.bodybuilding.com/fun/images/2015/safely-improve-your-shoulder-strength-and-mobility_graphics-pec-lacrosse-ball-rollout.jpg).
Grieve et al. (2015) has determined that self-myofascial release can lead to increased mobility.  Facilitating proper mobility in the shoulder comes from developing stable and healthy soft tissue in the decelerating muscles, anterior supporting muscles, muscle superior and caudal to the joint cavity, as well as the muscles allowing for overhead reach, including the serratus anterior, and the latissimus dorsi.  With a study by Fronek et al. (2015) stating that shoulder injuries in minor league pitchers is significantly prominent, and may require invasive surgery and/or noninvasive treatment to regain proper functionality after an injury, it is important to take the time to do some form of self-myofascial release, in an effort to prevent shoulder injury in muscle, fascia, ligament, or elsewhere in the joint cavity of the shoulder.
A foam rolling series can be found by Eric Cressey, specializing in elite baseball development. Among the many benefits of increased mobility through self-myofascial release, the scapula can properly rotate on the rib cage, allowing for full range of motion and upward rotation of the scapula, as seen in the attached blogs by Eric Cressey.  The bottom line is, if you are looking to prolong a healthy shoulder cavity as an overhead athlete, self-myofascial release, whether by a foam roller, lacrosse ball, tiger tail, or some other form of active release, it is a crucial and commonly overlooked aspect of baseball development.

Videos to check out:
https://www.youtube.com/watch?v=EVp8gbkwFT8
https://www.youtube.com/watch?v=KzcZmQkKFmk
https://www.youtube.com/watch?v=8caF1Keg2XU
https://www.youtube.com/watch?v=r4AaVMYg_6o

Articles to read:
http://scholarship.shu.edu/cgi/viewcontent.cgi?article=3048&context=dissertations
http://ericcressey.com/corrective-exercise-why-stiffness-can-b-a-good-thing
http://ericcressey.com/tag/foam-roller
https://www.drivelinebaseball.com/2014/12/11/hacking-kinetic-chain-sample-chapter-full-table-contents/ (Hacking the Kinetic Chain; Mobility and Activation: Pre-Throwing and Post-Throwing Training)

Bibliography and Work Cited

Al Dajah, S. B. (2014). Soft Tissue Mobilization and PNF Improve Range of Motion and Minimize Pain Level in Shoulder Impingement. Journal Of Physical Therapy Science, 26(11), 1803-1805. doi:10.1589/jpts.26.1803

Cools, A. M., Johansson, F. R., Borms, D., & Maenhout, A. (2015). Prevention of shoulder injuries in overhead athletes: a science-based approach. Brazilian Journal Of Physical Therapy / Revista Brasileira De Fisioterapia, 19(5), 331-339. doi:10.1590/bjpt-rbf.2014.0109

Fairall, R. R. (2016). Acute effects of self-myofascial release and static stretching on shoulder range of motion and performance in overhead athletes with glenohumeral internal rotation deficit. Dissertation Abstracts International, 76,

Fronek, J., Yang, J. G., Osbahr, D. C., Pollack, K. M., ElAttrache, N. S., Noonan, T. J., & … Yocum, L. A. (2015). Shoulder functional performance status of Minor League professional baseball pitchers. Journal Of Shoulder And Elbow Surgery / American Shoulder And Elbow Surgeons … [Et Al.], 24(1), 17-23. doi:10.1016/j.jse.2014.04.019

Grieve, R., Goodwin, F., Alfaki, M., Bourton, A., Jeffries, C., & Scott, H. (2015). The immediate effect of bilateral self myofascial release on the plantar surface of the feet on hamstring and lumbar spine flexibility: A pilot randomised controlled trial. Journal Of Bodywork And Movement Therapies, 19(3), 544-552. doi:10.1016/j.jbmt.2014.12.004

Gulotta, L. V., Lobatto, D., Delos, D., Coleman, S. H., & Altchek, D. W. (2014). Anterior shoulder capsular tears in professional baseball players. Journal Of Shoulder And Elbow Surgery / American Shoulder And Elbow Surgeons … [Et Al.], 23(8), e173-e178. doi:10.1016/j.jse.2013.11.027

Healey, K. C., Hatfield, D. L., Blanpied, P., Dorfman, L. R., & Riebe, D. (2014). The effects of myofascial release with foam rolling on performance. Journal Of Strength And Conditioning Research / National Strength & Conditioning Association, 28(1), 61-68. doi:10.1519/JSC.0b013e3182956569

Stecco, A., Stern, R., Fantoni, I., De Caro, R., & Stecco, C. (2016). Fascial Disorders: Implications for Treatment. PM & R: The Journal Of Injury, Function, And Rehabilitation, 8(2), 161-168. doi:10.1016/j.pmrj.2015.06.006

Thomas, S. J., Swanik, C. B., Swanik, K., & Kelly, J. D. (2013). Change in Glenohumeral Rotation and Scapular Position After a Division I Collegiate Baseball Season. Journal Of Sport Rehabilitation, 22(2), 115-121