"Subscapularis Strain from Swinging a Baseball Bat in an Adolescent with Closed Physis"- Higgins et al, Sports Health 6-11.
The top picture represents a "traditional" exercise for the subscapularis. Sounds practical, right? I mean the subscapularis IS an internal rotator of the shoulder, no? Not as simple as you think. Especially in batting, yes the shoulder is going through external rotation, which is loading this muscle. The conundrum is the muscle originates anteriorly on the scapula...which is moving on the rib cage...which is also moving in the same direction, but at different speeds. BTW, just like my previous post, the injury occurs no where near end range.
Here's an exercise that simulates the function of the subscapularis in batting. Begin in the traditional pushup position. As you begin the descent, sneak your right leg under the left, enough so that you feel the pelvis rotate, without it touching the ground. Return to the starting position and repeat. The bottom picture represents a "tweaked down" version of the same exercise, that might be used earlier in the rehabilitation process.