It's an ironclad rule of baseball that there are never enough catchers. This makes intuitive sense -- at most positions you can get by with one player, but at catcher, except for the 1970s and early 80s when teams thought it was a good idea for players like Johnny Bench, Thurman Munson, and Gary Carter to catch 150 games a year, a team needs at least two functional receivers to get by. The closer the second-string catcher is to being of first-string quality, the better of the team is, because even with a fully healthy season by the starter, given judicious handling, the reserve is going to bat over 100 times.
Of course, that standard is almost never met.
There's something fascinating about back-up catchers, players who, by the nature of their position, are almost always the last player called upon to enter a game due to fear that the team will run out of catchers. If you're unfortunate enough to be a third catcher -- a rarity now that relievers have eaten away at the 25-man roster like a conquering cancer -- you may as well wear a sign on your chest that says, "Break glass in case of never," so strong is a manager's fear that with the first catcher out of the game, the second will be hit by lightning and he'll be forced to go to his "emergency catcher," usually a utility infielder who last strapped on the tools of ignorance in Little League. There's an old saying along the lines of, "Do you know what they call the guy who graduates last in his class at medical school? Doctor." This is true of reserve catchers, too; they're still major leaguers, but in some cases, only barely.
In short, reserve catchers are like reserve parachutes: you have to have one, but you really hope you never have to use it.
Perhaps a quarter of the major league teams don't face something like an apocalyptic fall-off in production when the starting catcher is out of the lineup; those teams have a clear advantage over competitors who have to roll out, say, Drew Butera, when the starting catcher is out of the lineup. Even when, as with the Indians, Twins, and Giants, the starting catcher plays at first base or another position on his day off, the reserve is still displacing a more robust bat at first base-in effect, the Giants' Brandon Belt platoons with Hector Sanchez (potentially one of the better bats among the reserve classes without quite being of starting quality), not Buster Posey.
This has long seemed to me to be underrated aspect of team-building; in a sense, reserve catchers should be among the highest-paid players in the business. If a postseason spot can be lost by as little as a single game -- and we know that happens all the time -- the back-up catcher, considered little more than a spare tire, is one of those places where a team can steal an extra win. David Ross, now with the Red Sox, was worth almost exactly five wins above replacement* (Baseball-Reference formula), or one win and change a season, during his four seasons with the Braves. No Brian McCann? No problem! Ross was on hand to protect McCann from tough lefties and the Braves from traditional catch-and-throw backstops.
*Research into catcher defense -- game calling, framing, blocking, etc. -- actually suggest Ross might have been worth almost five wins in 2012 alone, so reliable is his glove. Scoff away, but teams are scooping up data analysts in this particular field left and right.
Photo credit: Steve Mitchell-US PRESSWIRE
Problems of budget and morale make it impossible to sign to two starting players at every position. Trust me -- George Steinbrenner tried to force about 10 players into five positions (the three outfield spots, first base, and designated hitter) in the early 1980s -- and it doesn't work; everyone gets confused about their roles, morale goes to hell, and it turns out that having seven designated hitters doesn't do a damned thing to improve your pitching staff. We can't fault today's Yankees for not having a second Mark Teixeira on hand to replace the broken one, but catcher is different. It's the position where, virtually by definition, you know that you're going to need a quality replacement. If you think about the value of banking that one win, the one that could get you into the big dance, and you knew before the season that you could get a win that win in a way that most other teams couldn't, well, now you know why the Red Sox effectively doubled Ross's salary to make him Jarrod Saltalamacchia's back-up and platoon partner for 60-odd games.
So now we get into problems of scarcity. A few years ago, I suggested that teams should look to convert mediocre corner infield prospects to catchers; there is a short but noteworthy track record of very late conversions, including John Wockenfuss, Gene Tenace, and Bob Brenly, as well as Jorge Posada, who was converted from the middle infield. All four of those players were predictably low-rated defenders, but provided above-average offense at the position. Posada was used almost exclusively at catcher until the very end of his career, but his three predecessors were spotted around the diamond to get their bats in the lineup, something you never saw with Kevin Cash or Sal Fasano.
Team's naturally gravitate towards defense when selecting a catcher, and that makes sense to an extent, but it's the rare catcher who hits like a reserve catcher that gets to start for very long -- Henry Blanco may still be chugging along at 41 because of his defensive chops, but if you're the Blue Jays, you don't want to see his name in the lineup too often. Again, the difference between catching reserves and substitutes at any other position is that you know in advance that they're going to be overexposed. That being the case, it makes sense to give up a little defense for a lot of offense.
Perhaps the valuation of catcher defense as it influences WAR still has a way to go to be considered definitive, but it seems clear that a little defense does not make up for a lot of outs. In trying to emphasize offense at the position, teams have nothing to lose but their Quadruple-A first basemen.