Almost 4 years ago, I wrote an article that was sort of a spit-balled take on an arm action sequencing concept. Practically immediately, it was torn apart by Dr. Mike Marshall. I realized then that the article was poorly written. Part of that was the spit-ball nature of it, its kind of "thinking out loud" approach, but a big part was my wonderfully awful descriptions of and references to the kinetic chain.
Shortly thereafter, I threw a disclaimer at the top and promised to re-write the article. Well, there really isn't much point because, even cleaned up, I don't think the concept holds water. [UPDATE 2019: ... or does it?]
Today, at Ron Wolforth's Pitching Central Ultimate Pitching Coaches Boot Camp, that exact article was mentioned in reference to an analysis of different types of lay back, what causes lay back, and how someone can have late forearm turnover and avoid the dreaded reverse forearm bounce.
It's an action that I've addressed before in my pitcher analyses. In my analyses (both professionally and on this site), I've drawn attention to when a pitcher decreases reverse forearm bounce by "picking up" his elbow. You can see this very well in my 2009 analysis of Brandon McCarthy. Back then, I described it like this:
It's hard to tell from this angle, but McCarthy's reverse forearm bounce might be exaggerated by some elbow flexion. By this, I mean that he picks his elbow up high enough that gravity plus natural elbow flexion - rather than inertia - appear to be causing some of the ball's downward motion. This view is inconclusive, but I don't believe his ulnar collateral ligament would hold up for very long if inertia alone caused a bounce that large.
You probably noticed that I was having trouble effectively articulating my thoughts about it. Chris Holt of Pro Bound USA in Clearwater, FL [2019 UPDATE: now pitching coordinator for the Baltimore Orioles] -- who didn't know I was in the audience -- has solved this problem for me by calling it "elbow roll-in". If someone before him coined the term, I'd never heard it.
With that term in mind, watch some of those McCarthy pitches again. Pay attention to his elbow and layback. While there is almost definitely an intertial lag component that helps with McCarthy's layback, the bulk of the layback was done by the way he rolled his elbow into position to lead his forearm.
This method of layback is something for which I've become a big proponent over the past 4 years (for a number of reasons that I don't have time to get into right now). I've needed a succinct way to describe it for some time, and now I have it.