As Casey Stengel famously uttered after the 1962 expansion draft, “you have to have a catcher because if you don’t you’re likely to have a lot of passed balls.” Thus, Sandy Alderson aptly noted this week, the Mets as currently constituted are awfully thin at catcher. Josh Thole goes into the offseason as the only catcher under contract for next season. So, what should the Mets do?The first question, it seems to me, is what can Mets fans expect out of Thole? On the surface, Thole would seem to be an ideal “Moneyball” catcher. He shows great patience, with a 10.5% walk rate in the bigs last year, resulting in a .277/.357/.366 triple-slash line and a respectable .275 TAv. But there is a pretty big question. Namely, what happens if pitchers decide to simply throw Thole strikes, knowing he lacks power, thereby limiting his ability to get on base via walks?To illustrate how little power Thole has, allow me to add another statistic to our toolbox: Isolated Power or “ISO.” ISO is similar in some ways to slugging percentage, as it measures a hitter’s power using extra base hits. Unlike slugging percentage, however, it does so on a per at bat basis. The formula for ISO is fairly simple: ISO=(doubles + (2 * triples) + (3*HR))/AB. Its biggest flaw in my mind is weighting triples more than doubles, (which are more a function of speed than power) but so be it. Anything above .150 is pretty good. Jose Bautista led the bigs with an amazing .357 ISO in 2010. In any event, Thole’s ISO in 2010 was .089 at the big league level; although it was .164 at Triple-A. Thole’s ISO was “good” for 30th among catchers last year. Needless to say, that’s not a lot of power. It’s hard to be good with that low of an ISO, particularly if you can’t steal bases. In fact, of the 60 players (min 200 PA’s) who had ISO’s lower than Thole, only Ichiro and Jamey Carroll had TAv’s above .280. And nearly everyone on the list of low ISO’s is either a speedster and/or a great defensive player (or is Luis Castillo). Thole, of course, is neither.The above said, good catching is really hard to find. Last year, NL catchers combined for a .253/.326/.388 line. The Free Agent pool isn’t filled with stars, and to my knowledge, no elite catchers are available for trade.So, what should the Mets do? Well, here’s some good news. Josh Thole does seem to have some more power against righties. In Triple-A last year, his ISO against righties was a more robust .155, and for the Mets it was .103.The best answer, then, is to find a right-handed catcher who a) hits lefties well, b) is a decent or better defender, and c) has some pop (to balance Thole somewhat). Here are stats from 6 free agent catchers (not including Victor Martinez, whom I assume the Mets can’t sign), names disguised for a moment, and one catcher who has been mentioned as a non-tender candidate:PlayerCareer vs. lefties2010 ISO2010 CS%Free Agent A.229/.283/.413.20815%Free Agent B.279/.359/.471.24121%Free Agent C.262/.325/.398.09634%Free Agent D.193/.275/.267.09728%Free Agent E.263/.338/.427.10837%Free Agent F.284/.318/.503.18042%Non-Tender A.294/.405/.444.08539%Let me add two more pieces of relevant information: Free Agent B has two world series rings and Non-Tender A, in spite of his career numbers against lefties, had a .235/.353/.329 line in 2010. By now, you’ve probably figured out that Free Agent B is Jason Varitek. Non-Tender A is Russell Martin. The rest of the names are: Rod Barajas (A), Gerald Laird (C), Matt Treanor (D), and Miguel Olivo (F).Based on the above list, it should be no surprise that I would narrow it down to Varitek and Olivo. Now, to help us decide, two more stats. Varitek’s ISO against lefties last year was an amazing .370. Olivo’s numbers at home last year (Coors Field) .318/.349/.556; on the road, a meager .211/.276/.322. Citi Field is not Coors Field, even post-humidor, and therefore it isn’t realistic to expect Olivo to put up good numbers as a Met.So, I would recommend Varitek. If his playing time is limited, and focused primarily on lefties, as it would be in a platoon with Thole, he can still be highly valuable. There is also the intangible factor (yes I know, I’m supposed to be Saber guy, but if intangibles matter anywhere, it’s at catcher), “Tek” has a well-deserved rep as a great handler of pitchers, and, of course, is a winner. And if Tek decides to re-up with Boston? Then I suggest a Rod Barajas redux. He has pop, was good in the clubhouse, has shown he can hit for power at Citi Field, and when healthy, was effective last year.Let me address one criticism that I know will pop up in the comments: that Thole needs to play “every day” to develop. That’s wrong for a few reasons. First, Thole is a catcher and catchers just don’t play every day; and in fact per a baseball prospectus study do far better with more rest. Second, Thole is a very advanced hitter, it seems unlikely he’s really going to get significantly “better” against lefties. Third, Thole’s upside, because of his lack of power and speed and mediocre defense, means it’s unlikely he’s ever going to produce numbers that really warrant being a starter on a championship-caliber club.Finally, let me suggest a dark horse from the ranks of minor league free agents. Also from the Red Sox organization, Dusty Ryan. Ryan only hit .199/.333/.349 at AAA last year, but those numbers are deceiving. He hit .296/.412/.500 post all-star break with a .204 ISO and in 2009 at AAA he hit .257/.359/.455 with a .198 ISO. It may be possible to sign both Varitek and Ryan, and if so, given Varitek’s somewhat advanced age, would be worthwhile.Should the Mets follow this course, they would likely be left with a low-cost catcher tandem capable of above average production.