My good friend, Will Carroll of Baseball Prospectus, sent me some interesting observations on Mariano Rivera over the weekend:

Rivera ... watch his elbow for two things to see if he's going to be
good or crappy on a given day. If it gets up, almost even with his
shoulder in the "power T" position as he begins his trunk rotation,
he's good. If it stays up as his trunk rotates and is even with his
shoulder or slightly higher as he releases, even better.

He's dipping it lately, indicating fatigue. Brantley had a pretty
good breakdown on BBTN, but only covered the release point.

OK, cool. The only question I had was: What is the "power T" position? Will responded:

Oops ... ok, let's give the quick course on pitching mechanics. I
should do an article on this.

Pretend you're pitching. As you stride, your glove hand comes up and your back arm lifts and rotates. At the point where your front foot strikes, your arms should be straight out, putting both elbows on level with your shoulders. That's "power T".

From the power T, you will rotate your trunk - turn your body-bending slightly, pulling your arm through as fast as possible.

If he dips his elbow, the plane of his cutter gets flatter, rather than going in and down, it just goes in. It also puts more stress on his shoulder.

Will is right, he should do an article on pitching mechanics. I know I learned something I didn't know. It is part of what makes Carroll such a great guy. Like many other baseball writers and bloggers, he loves to share information. After all, what fun is there in knowing everything and keeping it all to yourself? I feel like I learn something new about baseball each and every day of the year. It's why I keep coming back for more.