The majority of injuries in pitchers are due to improper mechanics and overuse. Most of the time, if you know the injury, you can narrow down the type of poor pitching movement that caused the injury. It is important for the Athletic Trainer and coach to work together to correct the pitching motion and resolve the injury.
I have also experienced seeing a pitcher use poor mechanics and bringing it to the coaches attention to prevent injury.
A common injury due to poor pitching mechanics is a biceps strain. The triceps creates the force to throw the ball; the biceps job is to decelerate the arm after the ball is released.
If the pitcher does not follow through with the arm (stops short) a strain is put on the biceps causing injury.
I think that injuries occur as often in the acceleration as they do in the deceleration phase.