Although Rivera did have elbow surgery (not Tommy John) in 1992, he still not had developed his cutter, so there is no direct link to Rivera's elbow problems and his cutter. As Toby put it “I still want to see evidence of the cutter's strain on an elbow.” I have yet to hear that throwing a cutter can cause arm problems. It’s all based on the individual’s mechanics, and really every pitcher is one pitch away from some sort of arm injury.
Let’s look at Mejia’s mechanics:
Mejia is very balanced as he initiates his leg kick. As Mejia separates his hands, you can see the long arm swing that Warthen spoke of. This long arm swing can cause timing problems, which result in command issues. Mejia drives towards the plate with great force, using his lower half well. As his front foot lands, his throwing arm is a little late, as I spoke of earlier. You can see the strain he puts on his shoulder, as his arm tries to catch up with his front-side. The only way Mejia has any chance to catch up to his front-side is with a lightning quick arm. Notice how his glove side rotates powerfully to allow him to get to release point. Mejia does not get extension at release point, and this may be the cause of the natural cut on his fastball. That to me is the biggest difference with Mejia and Rivera. Rivera intentionally cuts the ball, while the ball just comes out of Mejia's hand with cutting motion.
Mejia has broad thick shoulders, which tells scouts that he can be durable enough to be a starter. Mejia has shown to be a very good athlete which allows him to repeat his delivery. That is a major plus. One could sum up Mejia’s mechanics as fluid and powerful. To his credit Warthen does acknowledge that others in the organization believe Mejia can be a starter long-term. Certainly Warthen knows pitching better than I do, and I will not knock the man for his opinion, I was very shocked to actually hear his opinion so openly about the organization’s top pitching prospect.
Now let's take a look at Rivera's delivery. Mind you in this video, Rivera is not at game speed, but still shows us enough to discuss.
The first thing that we see with Rivera is how fluid, smooth, and effortless his delivery is. Rivera has mastered the art of repeating his delivery. An infielder by trade, Rivera is a superior athlete, which allows him to repeat his delivery effortlessly. Rivera has a long arm swing as well, but is more efficient in getting his hand to release point. If you notice, Rivera's release point is out in front of his body a lot more than Mejia's release point. Rivera gets tremendous extension at release point, using his wrist and long fingers to get that cutting action on the baseball. The NY Times does a great job of dissecting Rivera's cutter.
The comparison between the shoe-in Hall of Famer Rivera and the young Mejia are ridiculous. The one big common trait they share is the fact that both have cutting action on their fastballs, even though they get this action in completely different ways.
What would Warthen have to say about this guys mechanics? (This is Hall of Famer Juan Marichal)