Fox as catcher?

jakefsu over at wpbc had an interesting idea about what to do about the backup catcher situation. Namely, why not carry Jake Fox as a backup catcher?

Now, I very much believe that Fox’s defensive shortcomings are serious enough that he’s well deserving of bench player status. However, I’m not sure I can be convinced he’s such a bad defender that there is simply no room for his bat on the big league roster. If the Cubs were to go ahead and give the 25th roster spot to Fox, he could back up both Soto at catcher and Aramis Ramirez at third while providing a much needed source of right-handed power off the bench, effectively addressing three legitimate needs with one roster spot. I mean, as long as we are talking about the last spot on the roster, why not try and get as much utility out of it as possible?

Before I get into analyzing their catching abilities, I just have one quick thing to say - if Fox is backing up Soto then it's highly unlikely that he will see many PH appearances. Managers are loath to PH with their backup catcher because of the fear that the starting catcher would need to leave the game, leaving no one who can catch.

Moving on to the main question at hand, the question here is whether Fox can fake catcher well enough to pick up some innings in the major leagues. His offensive contributions (wOBA projected at .327) would certainly be better than Koyie Hill (wOBA .293) or, God forbid, Paul Bako (wOBA .260). I'll be the first to admit that I know very little about Catcher defense numbers, especially in the minor leagues. So let's do a (very uncientific) comparison between the minor league catching numbers of Fox, Hill, and Soto, since they all have data at minorleaguesplits (this is from 2005-2008). The defensive value is calculated using Colin Wyers's catcher defense valuations, which used data from the major league level rather than the minors to figure out averages. To get the correct minor league ones we'd have to look at all the minor league data, which I don't have/am too lazy to generate. But, this is just a rough cut, and the same errors should appear in all three of their data sets.

Player	Innings at C	Sb	CS	SBA/9	CS%	WP+PB/9	Defense Score/150
Jake Fox	1380	137	53	1.239	28%	.9650	-18.5
Geovany Soto	2192.3	197	60	1.055	23%	.5049	-3.16
Koyie Hill	1509.3	102	46	.8825	31%	.4946	1.54

What do we see? As we can see here, people ran like crazy on Fox, and he was not good at blocking pitches. Let's see how Hill and Fox compare. Let's assume that Fox also picks up the extra 60 PAs or so that I have Miles due for at 3b, since he's a better hitter than Miles. Let's make the wild assumption that he would be league average at 3b defensively (he's no slouch at 1b, at least...I don't know the usual positional adjustment - if someone knows it would be great if you can help me out). I put a range of defensive numbers out there just to see what would happen.

Player	PAs	wOBA	Defense	WAR
Hill	100	.293	1.5	0.1
Fox	100	.327	-18.5	0.1
Fox (3b)	60	.327	0	0.2
Fox (3b)	60	.327	-10	0.1
Fox (3b)	60	.327	-20	0.0

Even if he is completely atrocious with the glove at 3b, this would not be a bad idea (he just wouldn't play 3b, and still have roughly the same value as Hill). Of course, this is just nitpicking over the backup catcher position (and 3b), and Fox would not be likely to see many PAs behind Soto and Ramirez. But hey, a run is a run, and if something were to happen to Ramirez I'd much rather have Fox backing him up than Miles. It would be great if he got lots of reps in at 3b in the minors, because at this point it's his most obvious route to regular time in the majors with this team, should anyone on the roster get injured.

(EDIT: the final defensive numbers I originally posted were not correct - they are aggregate numbers for the entire sample of minor league seasons that I used. This has been corrected.)

(EDIT2: I fixed the defense score to normalize it over 150 games (1350 innings))