Throwing side arm as you can see in the picture above causes excess stress on the arm. The reason not to throw sidearm is to avoid arm pain and forced inflammation of the tendons by them rubbing on the elbow ligament joint. As you can see Byung-Hyun Kim has an inverted W which is the first sign that the pitcher must over compensate to release the ball out in front of his body once his arm catches up to his body after hip rotation, further putting stress on the elbow if the front hip and shoulder is not aligned toward the catcher. If for instance the pitcher has a closed front hip or has his lead foot pointed inside to a right handed hitter he must also throw across his body to reach a target on the outside of the plate. Byung-Hyun Kim didn’t last long after his implosion giving up world series home runs in back to back games against the Yankees before having arm issues and further being released.