I was doing a little reading on Dellin Betances this morning, and was reminded that he had TJ surgery at the end of 2009. This was disappointing to me because Betances was one of my favorite Yankees' prospects. He's a 6'8", lanky, hard-throwing right-hander from the South Bronx, and he has oodles of upside. Unfortunately, he's been unable to stay healthy.
This led me to remember another Yankees' prospect, Brett Marshall, who was the Yankees 6th round pick in 2008 who had an inconsistent debut in Single A ball as a 19-year old. Despite that, Marshall remains a very high upside prospect for the Yankees.
I don't want to bite Baseball Intellect's material, so I'll simply point you in their direction for a great read on Marshall's mechanics in high school. It's certainly possible that the Yankees' minor league staff made some changes to his mechanics, but given their seemingly poor record with prospects and TJ surgery, I tend to doubt it. Here's BI's gif of Marshall throwing:
There's a lot not to like. Everything's out of joint, timing wise. He elevates his pitching elbow far above his shoulder. His pitching forearm isn't vertical at footstrike. He hyperextends his knee at footplant, thereby increasing the load on his knee. It's obvious that Marshall was an injury risk; the question is whether he would make the necessary alterations to maintain his health. The other big question is whether he's even able to throw with decent velocity and control without employing the risky mechanics that he does.
We'll have to wait to find out. Marshall had Tommy John surgery at the end of 2009.