Shoulder injuries are among the most frequent injuries in crossfit and other sports like gymnastics, weightlifting, bodybuilding, etc. There are multiple things that can contribute to these injuries, but in general it comes down to 4 key factors:
Flexibility
Strength
Volume
Technique
Flexibility
You have to have shoulders that can move. Movements like pressing over head, snatching, pullups, etc all require shoulders that can go through a full range of motion. This is because of how your body has to work around inflexibility to get the job done. You will have big changes in technique in order to compensate for lacking motion. This places a lot of stress on things like the shoulder joint itself, the rotator cuff, the bicep tendon, the labrum of the shoulder and even the joints of the elbow. The usual culprits are:
Tightness in the lats and upper traps
Stiffness of the thoracic spine
Overdeveloped chest and anterior shoulder muscles
Stiff ankles and hips can also be a factor for movements like the overhead squat and snatch
Strength
When we talk about strength, we aren’t talking about how much you can bench or lift overhead (at least not usually.) We are talking more about having shoulders that are balanced. We do a lot of overhead pressing, horizontal pressing and overhead pulling. What we don’t do a lot of is training the muscle groups on the back of the shoulder and upper back. This is the infamous rotator cuff that many people hear about. When we have strong muscles on the front of the shoulder and weak muscles on the back side, your shoulder is going to be pulled into bad positions and affect your technique, as well as put a lot of extra stress on the structures on the front of the shoulder. You need more training of muscle groups like:
Lower traps
External rotators
Lats
Strict gymnastics strength prior to kipping
Volume
You could have excellent flexibility and strength, but if you are doing way too much volume of shoulder training you may still find yourself in trouble. A good example is athletes that do a really intense shoulder workout like Murph, without much preparation in their training. Doing too much, too soon. It’s just like runners that start ramping up their mileage too quickly. We have to make sure that we are recovering from the work we are doing and progressing it slowly over time to avoid overloading the shoulder.
Technique
How you do something is just as important as how flexible or strong you are. Using bad form on movements like kipping pullups, toes to bar, muscle ups, bench, pushups, overhead lifts, etc. is one of the quickest ways to find yourself injured. Listen to your coach, check your ego, film yourself performing the movement and take the time to practice your form at lighter weights.