Tom Tango has found that the worst defensive catcher all time (Mike Piazza) was worth -10 runs defensively during any given season. Tango also found that the best defensive catcher (Ivan Rodriguez) was worth 10 runs defensively during any given season. That means the difference between the best and worst defensive catcher is a total of 2 wins. Catcher is an extremely difficult position to play, but those who can make it to the majors fall into the -10 < x> 10 run spectrum of defensive talent.

Honestly, I don't foresee John Jaso becoming the Rays back-up next season unless Shawn Riggans gets hurt. That means I foresee John Jaso becoming the Rays back-up at some point next season, because Riggans cannot stay healthy. Above I've simply given Jaso the replacement and positional values that Riggans racked up this year, and thrown in a range of offensive and defensive values. Mix and match as you see fit, but the goal should be topping 0.5 wins.

Here's the problem, that win value isn't entirely accurate for Riggans.

Riggans defense was acclaimed in the minors, but that seems like undeserved hype, or at least a skill set that may not translate over to the majors. Below you see the career numbers for both Riggans and Piazza. The key for the table is pretty simple. INN is the career amount of innings caught, PB is the amount of passed balls, PB/INN is the rate of passed balls per inning caught, CS is caught stealing, SB is stolen bases taken, and CS% is ...well do I really need to explain that one?

Riggans has about 1,300 innings of catching before he matches the sample size, but given the numbers here, he won't get a chance of achieving such. Riggans is allowing more successful steals and passed balls. Now, unfortunately, we don't have much minor league data for Jaso to go off of, but if we assume that every game in he played a full nine as catcher -- unlikely, yes -- here's the results:

So, more passed balls, less stolen bases. How does these two match up in terms of runs? Well, after adjusting both lines to Riggans 2008 workload (~340 innings) I ran the linear weight values on PB, SB, and CS. Here's what we get:

We're assuming the following:

• Jaso's defense doesn't regress after being promoted.
• Jaso's innings total isn't too far off, skewing the ratios.
• Riggans defense hasn't been adversely affected thanks to injuries, and if so, he can stay healthy moving forward.
• I'm most concerned about the second point, but I can't find an exact total of innings. So here's what I decided to do: use percentiles, and find the amount of runs negated by the passed balls. See below.

I'm still not overly pleased with having to guesstimate, but it's a step in the right direction.

Of course there are other things catchers do: framing, blocking balls, game calling, calming pitchers down, tipping pitches, making the hitter less aware, ect. that we're not accounting for. In this rough sketch though, Jaso is closer to "bad, but passable" than "Is...is that an oven mitt?"

Am I insane, or does this make some sense?