So, having seen several people suggest that the Tigers sign Vladimir Guerrero to man the DH and play Victor primarily at catcher, I decided to do some analysis and see exactly what the Tigers would be gaining or losing from this proposition.
Last year, Martinez played 904 innings at catcher and Avila played 757. In VM's 904 innings he had 126 stolen base attempts, or one every 7.2 innings (That's seven and one fifth innings, not seven innings and two outs). In AA's 757 innings he had 63 stolen base attempts, or one every 12.0 innings. This means that VM faces approximately 67 percent more stolen base attempts per unit of time than AA. So, if VM logs 1458 (162 times 9) innings at catcher and has similar run on stats to last year, he'd face 203 stolen base attempts. If AA logs 1458 innings at catcher and has similar run on stats to last year, he'd face 121 stolen base attempts. If we divide these results by 162 we get the stolen base attempts per game for each catcher. AA's is 0.75 stolen base attempts per game and VM's is 1.25 stolen base attempts per game.
So, given that more runners try to steal on VM more often than AA, how does their throwing ability modify the amount of runners that advance?
Last year VM throw out 21 percent of runners, not far off from his career percentage of 24, but far better than the previous year's 14 percent. AA threw out 32 percent, and this makes up the majority of his MLB career.
So, given out stolen base attempt rates of .75 and 1.25 and factoring in the throw out rates, it's easy to calculate the stolen bases per game for each catcher. If you take the Stolen base attempt rate and subtract the sum of the stolen base attempt rate times the throw out rate you get the successful stolen base rate.
For AA that looks like this: 0.75 - (0.75*0.32) = 0.51 stolen bases per game.
For VM that looks like this: 1.25 - (1.25*0.21) = 0.99 stolen bases per game.
So, given last year's stats, VM allows, on a per game basis, nearly twice as many stolen bases per year. Extrapolating this over a 162 game season, AA would allow 83 stolen bases and VM would allow 160.
Now, I know that neither catcher will actually catch all 162 games, but I felt like this would help to illustrate how much better of a defensive catcher Avila is. There are a lot of other things to consider when looking at catcher defence, such as passed balls, errors, and, of course, pitcher handling. However, given the short duration of Avila's career, I don't have sample sizes required to make any significant insights.
Now, as to whether or not Vlad Guerrero's (VG) production would outweigh this loss is hard to say. Avila had what we all assume (Hope? Pray to Avila himself?) to be a down year last year at the plate, while VG continued to hit at high level. VG would have to hit at approximately a half base per game better (the difference between VM and AA defensively) than Avila for each game that VM replaces AA at catcher.
Last year VG had 643 total plate appearances. He hit 29 home runs, 1 triple, 27 doubles, 121 singles, walked 35 times, and was hit by 9 pitches for a total of 338 bases (338 = 29*(4)+1*(3)+27*(2)+121+35+9). He also stole 4 bases, so you could say 342 total bases. That's .53 bases per plate appearance.
Last year AA had 333 total plate appearances. He hit 7 home runs, 12 doubles, 48 singles, walked 36 times and was hit by 2 pitches for a total of 138 bases (138 = 7*(4)+12*(2)+48+36+2). He also stole 2 bases, so you could say 140 total bases. That's .42 bases per plate appearance.
Given that a starter will get about 4 plate appearances per game (last year Miguel had exactly 4 appearances per game, Inge had 4.02 per game, Carlos Guillen had 4.04, Peralta had 4.2 between Detroit and Cleveland, VM had 4.2 with Boston, Magglio had 4.3, and Jackson had 4.5), AA would get 1.68 (4*0.42) bases per game while VG would get 2.12 (4*.53).
The difference of .44 bases per game is really close to the .48 bases per game difference in Avila's and Martinez' catching defence, although it is less. Furthermore, it seems likely that AA will hit better than last year and it also seems possible that VG will slip a bit as he continues to age.
So, in the end, it appears that replacing Avila with Martinez and hitting Vlad in the DH spot is at best a wash. Especially if one considers that we don't necessarily need to look at this season in a vacuum and that Avila's continued major league development is important to the club and that Vlad will likely cost millions and millions of dollars.
Stats from Fangraphs and ESPN.