Aaron Crow, a Mizzou pitcher, seems to be getting quite a bit of press lately. Both Chris O'Leary and Saber-Scouting have written about him, the former disliking his arm action (showing signs of what Chris calls the Inverted W and Inverted L) while the latter likes his ability to scap load and his elbow picking up the ball.

Here's Aaron (image credit: Chris O'Leary's site):

While I would like to go on at length about his mechanics and will likely do so in the near future, I would like to point out that in this image, his arm is late in getting to the high-cocked or ready position at footstrike. He has an inefficient arm loading pattern and "loops" his arm, causing unnecessary stress on his UCL and rotator cuff muscles, specifically his pectoralis group.

Another thing of worry is his excessive reverse rotation in his shoulders and his wrist "hooking" the ball as he does so. Look at this animated image that the guys from Saber-Scouting put together:

I do not like pitchers loading their arm behind their back, instead preferring that pitchers break their hands straight down in a pendulum swing not beyond the acromial line of their body. This reverse rotation leads to the aforementioned timing problems of the arm getting up late and will contribute to injury down the line.

It's clear that many of the "preferred" video analysts follow a similar doctrine - they all like tempo into footplant (I agree), an "elbowy" arm action (strongly disagree), and don't focus enough on what causes arm injuries. Is it any wonder that pitchers who are praised for having an "elbowy" arm action consistently land on the disabled list with biceps tendonitis, UCL-related injuries, or shoulder impingement problems?

In general, I do not like his arm action nor his timing, and agree with Chris rather than Saber-Scouting on this pitcher.