I should add that what also contributed to my pondering of the issue is golf. I have--by no means--a textbook swing. But at my peak it allowed me to be a +1.8 handicapper and I can still average around 300-310 yards per drive. I move my left foot in my back swing, I sometimes step through the ball on follow through, I have a weak left hand and come absolutely nowhere close to parallel. Yet it works. When looking at it on video, it's easy to note that while it's unorthodox, I accomplish nearly all of the goals of "perfect mechanics" even though my swing does not look pretty. I wasn't trying to cherrypick with Sale, Bumgardner, or Kershaw. They all have uniqueness to their motion. But they all probably accomplish the goals of perfect mechanics at varying positions in their motions (with the golf analogy). An interesting thing you mention about how the baseball might be too light. Yes, it's about 35% of a football. That made me think about a softball. I never once had a sore arm as a kid playing baseball. But in college intramurals I would get severe pain from throwing a softball in the biceps region. I did have to alter my motion when throwing a softball--I wish I remembered what I did. Some guys are meant to get hurt. Two of the very best-pitched Brewers games I saw in person were thrown by Kyle Peterson. We'll never know if the mechanical changes caused the injuries. Stoutdude04 had a nice point...don't draft (at least early) guys with mechanics that you want to change. Also, semantics here, but didn't Mike Jones tear his UCL after he'd twice had shoulder surgery? Also, in the 90s it seems like we were constantly hearing "rotator cuff." For the last 15 years it's been UCL. For a while about 10 years ago labrums were always getting injured. Lately (since Sheets) we've been hearing about torn flexor tendons. Maybe diagnoses are just more precise, or maybe this is just perception. But it seems like the types of arm injuries have been parts of trends in the last 20 or so years. If there's something to my observation (no clue how to find evidence), then what does that tell us? Are teams more careful with shoulders now than they used to be? Is strength-training helping to prevent those injuries? Who were the last major star pitchers with rotator cuff surgery? I think Randy Johnson, Pedro Martinez, Ramon Martinez, and Alex Fernandez all effectively had their careers end from it, but in all cases they were relatively old with lots of innings. Seems like in the 90s "rotator cuff" was much more of a common injury than UCL.