Here is some excellent work from Baseball Prospectus’s Mike Fast. So, can we conclude that we'll generally call pitch framing accounts for about half the differences in catcher's ERA or just about all of it? Should we compare Fast’s numbers to Sean Smith’s regressed or un-regressed numbers?

Let’s go back to the old Angels catching controversy. If the best catchers save 40 runs a year and the worse add on that many, is it possible Steve Scioscia was correct to have played Mathis at Napoli’s expense all those years? Let’s say Smith’s 80 run difference is based on 120 games per year – the number Mike Fast used for comparing catcher’s runs saved by pitch framing. Let’s say 120 games produce 480 PA. Using career Runs Created as tallied in Baseball-Reference today (Sept. 21, ’11), over 480 PA Jeff Mathis has on average produced 35.25 runs. Over the same number of plate appearances, Mike Napoli has produced an average of 77.75 runs. The difference is just over 40 runs – half of Smith’s un-regressed numbers, but more than his regressed differences of +/- 15 runs (30). Keep in mind that is assuming Mathis is one of the best catchers at saving runs and Napoli is one of the worse. This article written by Sam Miller in the Orange County Register January 23, 2009 directly compared how the Angels starters pitched under Mathis and Napoli. While, Mathis did have a slight edge in K:BB%, but not HR%, if you take out Ervin Santana – who had Mathis as his personal catcher, while the other starters about evenly shared the two catchers – Napoli comes out slightly ahead – defensively!

In June of this year, Miller guested in Baseball Prospectus with this article on the same subject. Like Miller and the 24 BP readers who commented, this is a subject we can’t let go, despite Napoli having left Anaheim last winter. It is a subject worth looking into on any team; the Napoli/Mathis debate is just the most obvious extreme case. Perhaps, we should be crying that the John Farrell should have caught Jose Molina instead of J.P. Arencibia? It seems we only really notice this debate when the defensive catcher plays over the offensive catcher – no doubt because good hitting is more obvious thanks to the stats we see than good defense.

In Miller’s BP article, in an indirect flippant way, he makes the case based on all those preceding studies, that pitch framing may account for just about all the significant differences in catcher defense. Certainly the work that Mike Fast and Dan Turkenkopf did have solid evidence that Mathis did save an average of 16 runs per 120 games over Mike Napoli’s catching. That is still a long way from the 42.5 runs Napoli hit better in 480 PA.

Sorry, I have no further fancy concluding statement.