Without really crowdsourcing at all, I would imagine that a majority of tuned in Mariner fans were pleased with the John Jaso trade. As the M’s and their supporters are all too aware, finding a decent big league catcher isn’t easy, and the acquisition came with the added bonus of sending Josh Lueke out the door.

If there was any facet of the deal that made fans pause, it was the ease in which Jaso was acquired. We’re talking about a catcher who posted a 116 wRC+ in 2010 and has four years of team control left on his contract. Why did the Rays give him away for a marginally effective reliever with a well documented off field history?

The easy answer is that the Rays simply didn’t think Jaso was going to be effective going forward. Jaso was dealt to the M’s on November 27th, and considering that Jose Molina signed a deal with the club one day later, I’ll just go ahead and assume that they weighed the pros and cons of each and went with Molina. As to why the Rays opted for a career backup over a guy like Jaso who should, at least in theory, be in his prime, I think there were three main reasons.

First, Jaso’s defense isn’t very good. Catcher defense is difficult to quantify, but from what research has been done, Jaso doesn’t stack up well with the competition and he compares particularly poorly with Molina. Molina is one of the best in the business at throwing out runners (40% caught stealing rate for his career) while Jaso’s meager 19% CS rate doesn’t really deter anyone from trying to take an extra base.

Additionally, saberist Mike Fast (now employed by the Houston Astros) has done some research on pitch framing, and while defensive numbers should always be viewed with a hefty dose of skepticism, he found that Molina was the best in baseball at framing pitches. By contrast, Jaso was a below average receiver. If Fast’s estimates are correct, Molina is more than a win better than Jaso due to pitch framing alone.

Second, Jaso was never an impact prospect, and his major league breakout was something of a surprise. The Rays have a reputation for moving players through their farm system slowly, but Jaso’s pace through the minors was glacial. He was only an eighth round pick, but even the low picks that reach the majors tend to show their skills early and are promoted quickly. Jaso spent six and a half seasons in the minors before getting called up for good in 2010 and he repeated a level on three separate occasions. His minor league career is a lesson in perseverance but also serves as an indication that the Rays never thought terribly highly of him as a major league catcher. I’m not saying the Rays are right or wrong about Jaso: only that a quick review of his career suggests that the Tampa Bay brass still haven’t bought into his breakout from two years ago.

Finally, the biggest reason Jaso was available on the cheap is because he had a lousy year in 2011. Oftentimes a poor season  is a great buy-low opportunity, particularly when a player’s performance is hindered by injuries or extenuating circumstances, or when his peripherals suggest a rebound is likely. None of those appear to be at play with Jaso. Yes, he did visit the disabled list with an oblique strain, but he was already well on his way to a bad year at the plate when he went down in July.

Worse, a glance at Jaso’s peripherals indicate some concerning trends. A calling card of Jaso’s game is his selectivity at the plate: he walked in nearly 15% of his plate appearances in 2010 and that figure is backed by several similar percentages when he was a minor leaguer. He complemented his ability to take a walk with good bat control: he only struck out in 9% of his PA’s in 2010, and again, posted similar minor league figures. Those numbers flipped in 2011. In and of itself, that kind of a switch in both BB% and K% is unusual. For Jaso, it’s also unfortunate, because without any power, he needs to walk and give himself plenty of chances to get on via a base hit. Less walks and more strikeouts defeat both both objectives. And while it’s true that his numbers in 2011 were deflated by a lousy BABIP, a slow catcher who hits a lot of ground balls is a bad candidate to post a high figure in that department going forward.

Ultimately, Jaso seems more like a very good backup catcher and decent pinch hitter than a big league starter. In addition to his struggles last year, he’s neutered by lefties (.188 career batting average) and at age twenty-eight isn’t likely to get a whole lot better. That doesn’t mean he wasn’t worth acquiring: not by a longshot. He does hit righties pretty well (career 104 wRC+) and his defense is probably a little better than what Miguel Olivo and Jesus Montero can provide. If Jaso can prove that 2010 was no fluke, and that he can be a solid big league regular, Jack Z will have swindled another victim. But even if Jaso doesn’t have that kind of projection, he still can be effective in a platoon, and his bat off the bench can pay dividends for years to come.