Fatigue is a key factor. Muscle fatigue can affect mechanics and also the muscles holding the joins together under stress / torque conditions. Once the muscles you have worked on so hard start to fatigue and you continue to throw at top velocity, you are at a greater potential for a strain. The strain can be from lack of proper mechanics or from the joint muscles being fatigued. Lack of strength, conditioning, and flexibility can cause any number of strains in any body area. You can also over develop one part of the muscle, raising your risk of injury. The SS example is a good fatigue example. Comparing a position players infrequent hard throw to a pitchers 100 hard throws, you can see how fatigue can set in differently. If you are a pitcher, working the core hard, and are not doing the same with the upper body (not talking about rubber bands and stabilizing muscles - you need that as well), you are bound to have issues. You will generate too much torque on the elbow as you have mentioned.