A Wholly Unscientific Look at Matt Wieters's Defense Post-Tommy John

Before I get into this, I should stress that — as the title states — this is an unscientific article. As such, it shouldn't have any huge effects on anyone's appraisal of Matt Wieters, much less for the Orioles in 2015 overall. Unlike erstwhile Depot contributor Stuart Wallace, I don't study medicine, nor do I have any experience with injury analysis. I simply wish to compare Wieters's plight to those of players who have dealt with similar adversities.

In the campaigns preceding 2014, Matt Wieters had one of the better arms in the majors: From his debut in 2009 to 2013, he accrued 16 rSB, the most in the American League. Gunning down one in every three attempted base stealers, he provided as much value as he could behind the dish.

In the early going of last year, he began to show signs of wear. Of the twelve men who took off against him, eleven arrived safely; had he compiled enough innings to qualify, every other major leaguer would have topped that rate. He didn't qualify, though, because his season went from bad to worse: A damaged ligament in his right arm sent him under the knife, and put his future in doubt.

Many pitchers have undergone Tommy John surgery, and many people have written of its effects. (Their findings have tended to contradict each other.) But what about the hitters who have done the same? To the best of my knowledge, only two people have looked into the latter group: Jeff Zimmerman at RotoGraphs, and wafflechip27 at the FanGraphs Community blog. Both of those looked at hitting performance, though; I'd like to focus on the other side of the ball — throwing. What does the operation's history tell us about players' defense before and after it?

Because very few position players have undergone Tommy John surgery, I had a very small sample size with which to work. From Jon Roegele's Tommy John surgery database, I found 24 catchers (Wieters included) who had it. Of them, a few — Matt Clark, Dustin Houle, Matt Reistetter, Andrew Knapp, and obviously Wieters — have had the surgery within the past year-plus, and thus haven't had enough time back. Moreover, 12 of them didn't play much prior to having the procedure. Thus, I limited my scope to the five who remained.

What did I find? Well, only two of the guys accumulated significant major-league innings both pre- and post-surgery, and both of them fared pretty well going forward:

Player	Pre Innings	Pre CS%	Pre rSB	Pre rSB/1000	Post Innings	Post CS%	Post rSB	Post rSB/1000
Todd Hundley	5782.1	25.9%	---	---	2822.2	23.8%	---	---
John Baker	1538.0	19.4%	-10	-6.5	1032.1	17.7%	-3	-2.9

While neither Hundley nor Baker was particularly adept at throwing out runners after Tommy John, their rates of doing so didn't diverge much from their rates before it. Plus, they were of a similar age to Wieters when they had it done — Hundley was 28 (like Wieters), and Baker was 29. So this tells us that Wieters will come out of this as good as ever, right?

Well, no. Aside from the fact that two people don't exactly make for a large sample, this means of analysis has one fatal flaw: survivorship bias. By only looking at the catchers who made it back to the show, we get an incomplete picture. Instead, we should take into account all of the catchers who had major-league time beforehand, regardless of if they made it back or not. And bringing in the three other men changes the conclusions a little bit.

Ben Davis had 3631.1 innings and a 33.9% caught-stealing rate before falling victim at age 28. Returning to the minors the following year, he threw out a mere 20% of base stealers over the last five seasons of his career. Vance Wilson — he of the 2388.2 innings and 40% CS% across eight seasons — went under the knife shortly after turning 33. He would endure the surgery again a year later, and would only play 18 games at AA (in which runners went 20-for-20 against him). And Chris Coste, who owned a considerably more mediocre 22.1% clip in 1641.2 innings, took an early retirement once he went through the procedure (albeit as a 37-year-old). Taken together, these three detract from the relative optimism inspired by the previous two.

The ages of the five men (and the fact that, y'know, there were only five of them) obviously add some pretty significant caveats to this. Nevertheless, one shaky point remains: When a catcher has Tommy John surgery, his future value takes a hit. If Wieters hits the free agent market after 2015, will the Orioles bring him back? Considering the things I've learned in writing this, I'm not too sure.