The Mets acquired Kelly Shoppach from the Red Sox today for a player to be named later. Shoppach, a right-handed hitting catcher that’s not half-bad offensively, fills a need for the Mets: He can spell Josh Thole against lefties without creating a hole in the lineup. He’s not Johnny Bench on either side of the ball and he had back-to-back woeful offensive seasons in Tampa Bay in 2010 and 2011, but Shoppach has been a patient hitter with some pop in his bat for most of his career. He doesn’t make a ton of contact, but all things considered he’s about a league-average backstop offensively and represents an obvious upgrade over the woeful hitting the Mets have gotten from their backup catchers this season.

What’s odd is the timing. Shoppach is eligible for free agency after the season, so unless the Mets believe he’ll accept arbitration, he doesn’t factor in their plans for 2013. And though he makes the team ever-so-slightly better for the next couple of months, he’s hardly enough to catapult them back into the Wild Card race from nine games out.

The Red Sox called up prized catching prospect Ryan Lavarnway a couple of weeks ago, and they too are more or less out of the race. So maybe the move is about clearing room for Lavarnway to catch more often, and the Mets’ angle is something along the lines of, “Hey — free upgrade, why not?” But a lot depends on the quality of the player yet named, obviously.

For now, the Mets get a little bit better, which is nice. I suspect the move will make a bit more sense at some point in the future.

If you are a conscious human and fan of Major League Baseball, you probably know by now that the Mets’ bullpen sucks. And if you are not a conscious human or fan of Major League Baseball, it’s extraordinarily unlikely you are reading this blog. And that’s good, because if you’re not ready to get nerdy with this, you’re probably not going to care for this post.

If you’re interested in what follows, you might want to open up the league-wide bullpen stats at Fangraphs and Baseball-reference to follow along.

The Mets’ bullpen has the worst ERA of any relief corps in baseball despite playing half their games in a park that favors pitchers. It sucks, and we’re past dismissing it as confirmation bias at this point. It sucked at the beginning of the year, it sucked in the middle of the year, and it sucks now.

It’s worth noting, at the very least, that the Mets’ relievers have not allowed the most runs or the most runs per game — a couple other bullpens have been more viciously victimized, at least statistically, by their defenses. And the Mets’ bullpen, as difficult as this may be to believe, falls (barely) outside of the league’s bottom five in save percentage. So there’s some evidence that it’s maybe not quite as bad as we think it is, at least relative to the league.

Still, by Fangraphs’ shutdown/meltdown stat, the Mets have the only bullpen in the Majors that can boast more meltdowns than shutdowns. Even if the Mets’ bullpen is not blowing saves at quite the rate of the Rockies’ or Brewers’, it is more often allowing close games to fall out of reach than it is keeping them close. That’s kind of crazy, considering how much baseball in general favors pitchers.

And any qualifications of the Mets’ bullpen suckitude could only be used to argue that it doesn’t suck quite so hard as a couple other team’s bullpens, and even those arguments would be tenuous at best. There’s just no doubt that the Mets’ bullpen sucks, only a million open-ended questions about why it sucks to this extent. So with that in mind, let’s look at some possible explanations.

Poor construction: As good as Sandy Alderson has been so far at maximizing the fringes of the Mets’ position-player roster, he has been just as bad at putting together competent bullpens. It’s a tiny two-year sample, obviously, but if Alderson is hailed here and elsewhere for his moves that pay off, he should be faulted for those that don’t even if they were difficult to foresee. The GM is ultimately responsible for the personnel on a team’s roster, and the personnel in the Mets’ bullpen have not proven adequate.

Still, who saw this coming before the season? That’s not a rhetorical question; I’d love to see the reasonably argued column or blog post predicting that the Mets’ bullpen would be anywhere below capable. Multiple members of the group — notably Frank Francisco, Ramon Ramirez and Manny Acosta — have pitched way worse than their historical norms. Only Bobby Parnell and Jon Rauch have pitched better than their established levels, and only marginally so — not nearly enough to make up for the difference in their teammates’ performances.

A case could be made that the Mets entered the season relying on too many old relievers. Perhaps, given the sample sizes in which relief pitchers operate, by the time a guy can establish a level of production he is too old to maintain it. None of the best bullpens in the league include nearly so many pitchers on the long side of 30, and the Reds’ league-best bullpen has featured only one 30-plus pitcher all year.

But then, the Cubs, Cardinals and Astros all have bad bullpens with lots of young pitchers, and the few other big-league clubs that count on a handful of older relievers — the Blue Jays, Tigers, Angels and Giants — have all been OK. None have been great, which seems worth noting, but they’ve all been appreciably better than the Mets.

Plus, outside of Parnell, none of the young or youngish pitchers the Mets have tried in bullpen jobs has met with much success. There’s still hope for Josh Edgin based on his Major League peripherals, and some hope too for Pedro Beato, Elvin Ramirez and even Rob Carson based on their youth and Minor League numbers. But none of them was even an average Major League pitcher in their short big-league stints in 2012. You can’t just plug in young guys and assume they’ll be good, obviously. You need good young guys, and the Mets haven’t had many this year.

There’s no sure way to build a bullpen. It does seem like most great bullpens tend to be more reliant on arms developed in-house or acquired via trade than Major League free agents, but that’s certainly not a hard-and-fast rule. So while ultimately the blame for this bullpen must fall on Alderson’s shoulders, it’s hard to say with confidence that it’s all his fault.

They just suck: Well, maybe, but it’s hard to figure out exactly why. They walk a lot of guys, but not the most of any bullpen. They have a slightly below average strikeout rate. Their 1.47 WHIP is bad, but not as bad as the Cubs’ or Brewers’ (though both those bullpens are also bad).

The Mets are near the bottom in the league in zone percentage (pitches in the strike zone), and above only a couple of teams who generate a lot more swings-and-misses. So maybe there’s something there: They don’t fool enough hitters to get away with throwing so few strikes. But they are near the middle of the pack in line-drive rate and contact rate and in the low-middle range in home runs per fly ball.

There are a bunch of pitchFX and batted-ball numbers to show that the Mets’ relievers are underwhelming, for sure, but there’s none that really jumps out as an explanation for why they’re collectively so bad. At least by my understanding — if you’ve got something more definitive, please jump in and say something. I’m hardly an expert on this stuff.

Mismanagement: Early in the season, when the Mets were leading the league in relief appearances by a pretty wide margin, I was eager to pin the struggles on Terry Collins’ quick trigger. But as the Mets’ relievers have continued to struggle, Collins has reined in their use. They’re now merely sixth in the league in appearances, which seems rather remarkable given how often they need to be pulled for ineffectiveness. And the Mets are in the bottom half of the league in relief innings pitched and around the middle of the pack in pitches thrown. They’re sixth in appearances with zero days rest, but they’re below the Rays and Braves in that stat, and those teams have good bullpens.

At times, it has seemed like Terry Collins hasn’t helped things with constant reliance on platoon matchups and established bullpen roles, with some “dry-humping” to boot. But it doesn’t seem like any aspect of Collins’ management has been particularly egregious when you consider the performance of the men he has been charged with using.

Bad luck: There’s some evidence the Mets’ relievers have been unlucky this year. If you subscribe to DIPS theory, you might care to learn that they’ve got the biggest positive differential between their ERA and FIP of any team in the Majors — suggesting they’ve been better than their results and should in time meet with more success. Of course, they’ve combined for 319 2/3 innings this season, and though random fluctuations can play out over more time than that, it’s a reasonably large sample of collective sucking.

At 64.8 percent, the Mets also have the lowest strand rate (LOB%) in baseball, a stat that tends to normalize to around the league-average 72 percent. Part of that is likely because they don’t strike out a ton of hitters, but part of that is almost certainly bad luck. Fortune and randomness make for some of the least satisfying explanations for baseball phenomena, but they’re also very often the best ones. The Mets’ bullpen certainly hasn’t been good, but they haven’t been very lucky either.

Bad coaching: The Mets canned Jon DeBus as bullpen coach after one year last season and replaced him with Ricky Bones, but obviously neither has enjoyed much credit for their role. I have no idea to what extent a bullpen coach might help or hurt a bullpen, though — maybe they’re both really bad at pep talks or something, or they have terrible phone manners that somehow bother Terry Collins enough to make him antagonize his relief pitchers into being awful. That doesn’t seem likely, but hey.

Dan Warthen is the constant, and a constant bugaboo for Mets fans. I’d guess this season’s bullpen will cost Warthen his job, but I might have guessed that in 2008 or in 2011 and it hasn’t happened yet. Personally, I doubt Warthen’s coaching is what ails the Mets; the starting pitchers, after all, have been mostly very good when healthy this year. But since I can’t say for sure what effect a pitching coach has on a staff, I also can’t say if Warthen is good or bad at it.

Bullpen-wide malaise: If I’m trying my best to consider all the tangible explanations than I must consider the intangible ones as well. Maybe the Mets’ bullpen features awful chemistry or a defeatist attitude or some sort of bullpen-wide lack of accountability. Maybe they hate the starters and position players and want them to suffer. I don’t know. All of them seem like decent-enough dudes individually, and they’ve all pitched in better bullpens in the past. But maybe they lack a goofy vocal leader to rile them into effectiveness or something. I doubt it, but, again, hey.

So there’s no clear answer. I’m guessing the Mets’ bullpen has struggled due to a combination of nearly every factor above, with the possible exception of the last two. But then if I could say for sure what’s wrong with them, presumably someone in the team’s front office could too and he or she could get about fixing it.

There’s a lot of chicken-and-eggery here, but eight of the teams with the top 10 bullpen ERAs this season are in the thick of playoff contention, with only the otherwise-flawed Royals and Padres featuring good bullpens and bad teams. The good news is there’s enough randomness and fluctuation in bullpen performance and construction that we can legitimately hope the Mets’ bullpen is better next year, and that it’s good enough to help the team compete all season. The bad news is there aren’t a hell of a lot of guys in house who look certain to be part of that bullpen, so Sandy Alderson’s got a lot of work to do this offseason, and he hasn’t been great at building bullpens so far.