With the news of Mike Zunino's promotion all the way from low-A to Double-A came some peripheral questions about Jesus Montero and how long the Mariners will continue having him catch. He* did just allow three Tampa runners to steal second last night, though he also caught one. The answer to that, and similarly phrased questions, is of course, "we don't know." We aren't the Mariners. And even if we were, even if I were Jack Zduriencik or Howard Lincoln or Eric Wedge or Jesus Montero the answer would be "I don't know," because the future isn't known. You should probably stop asking that particular question.
*Assuming you assign 100% of the credit/blame for stolen bases to the catcher, which is dumb and wrong and stupid and shut up.
The better question to ask is "should the Mariners continue to have Jesus Montero catch?" That question doesn't require buckets of inside information or a universe-destroying time machine to debate. In this particular case, I don't know the answer to that either, but my opinion is yes, yes they should. Here are some reasons why.
First off, it's key I think to acknowledge that Jesus Montero is very young and not all that experienced. He's likely to get better, both offensively and defensively. He was new to the entire staff this season, thrust in to the middle of the Mariners batting order, and DHs a lot when he's not starting behind the plate. I don't think it is correct to expect him to be at his full defensive potential already.
That said, I also don't see numerical evidence that his current level is untenable. Measuring a catcher's defensive skill is hard and we only have a slice of the picture. I can hope that what we have is a representative slice, but there's no guarantee of that and for all we know Montero could be fantastic at coaxing borderline ball-strike calls or horrendous or average or purple. He might be great at pregame plans, pitch sequencing, calming down the pitcher and all the myriad of other things catchers do. He might be terrible at all of them too.
What we have readily available is how many passed balls and wild pitches are allowed under each catcher and how many runners advanced and were picked off trying to steal. Even those are imperfect, subject to imperfect and small sampling. But we have them and, acknowledging the assumption, we can at least look at how catchers compare. Here are 2012's numbers.
John Jaso: 236.2 innings caught, 10 WP+PB, 14 SB, 5 CS
Jesus Montero: 353.1 innings caught, 20 WP+PB, 35 SB, 9 CS
Miguel Olivo: 462.0 innings caught, 28 WP+PB, 38 SB, 18 CS
Or, scaling each of them to 500 innings caught:
Jaso: 21 WP+PB, 30 SB, 11 CS
Montero: 28 WP+PB, 50 SB, 13 CS
Olivo: 30 WP+PB, 41 SB, 19 CS
I feel it worthy to point out that total zone metric gives values (runs compared to average) of zero for Jaso, -4 (-6/500 inn) for Montero and -1 for Olivo. Looking at just the numbers that are available and make sense to look at (no, not you, cERA), I don't see a compelling argument that Jesus Montero cannot serve as the backup/job-share catcher for the near future.
Jesus Montero isn't a good defensive catcher, probably; at least from what we can tell. But he is young and more likely than not will get better. A big part of his deficiency seems to be making more accurate throws to second base and that can usually be improved on over time. More importantly to me, is that even at his current skill level, I don't see that he's a disaster back there, worthy of banishment to DH or a move to first base.