On Wednesday, the club finally took steps to address that concern, trading Jed Lowrie and Kyle Weiland to the Houston Astros for Mark Melancon.
Is Melancon the successor to Papelbon as closer? He saved 20 of 25 opportunities and posted a 2.78 ERA last season for the Houston Astros. The Red Sox acquired a key piece, but Melancon's role is still to be determined.
If Melancon does end up as Boston's closer, he'll represent a significant change from the overpowering Papelbon. Melancon's fastball averages 92.6 mph and tops out around 96. Compare that to Papelbon, who averages around 95 mph on his heater and gets up to 98.
So does Melancon have the stuff to be a closer in the American League East? (Feel free to ignore his 10.80 ERA against the AL East, a clear victim of small sample size.)
He won't blow hitters away like Bard does, but his fastball is effective in its own way. Opponents missed on 18.9 percent of Bard's fastballs. Melancon, despite significantly less velocity, had a 17.2 miss percentage on his heater. Perhaps more importantly, he threw it for a strike 69.1 percent of the time.
But enough about his heater. Melancon is really all about the curveball.
He threw 27.3 percent curveballs last season, easily the most of any closer. From a closer perspective, Melancon is more of a poor man's Heath Bell than in the Papelbon mold.
So what does history tell us about a closer who relies so heavily on a curveball? According to data on FanGraphs.com, the last closer to throw as many curves as Melancon did last season was Danny Graves (28.1 percent in 2002). For Red Sox fans, the most recent precedent was Tom Gordon.
Charting Mark Melancon's 38 curve balls that resulted in strikeouts.
In other words, it's not all that common for a closer to storm out of the bullpen and have batters quivering at the thought of an 82 mph curveball.
Then again, not many pitchers have Melancon's curve. It's not hard to understand why it is his out pitch.
He threw it 50.7 percent of the time in two-strike counts, the fifth-highest rate in the majors. Of Melancon's 66 strikeouts, 38 came on at-bats ending in a curve. When it's working, his curve drops right out of the strike zone. As the heat map at right shows, of those 38 strikeouts, 28 came on pitches below the zone.
Among relievers, only Jose Veras (64) and Sean Marshall (51) had more strikeouts via the curveball. In fact, Josh Beckett (60) was the only Red Sox pitcher with more curveball strikeouts, and those came on 204 more curveballs.
Just how nasty is Melancon's curve? Consider that only three pitchers held opponents below a .150 batting average on at-bats ending with the curve and also had both a chase percentage and miss percentage of at least 35.0 percent: Melancon, Roy Halladay and A.J. Burnett.
Highest Percentage of Curveballs Thrown in 2-Strike Counts (2011)
Jose Veras, Pirates
Daniel Schlereth, Tigers
Brett Anderson, A's
A.J. Burnett, Yankees
Mark Melancon, Astros
Poor mechanics on that curveball left Melancon needing Tommy John surgery just as his career was getting started. In college at Arizona, Melancon anchored a bullpen that included future major-leaguer Daniel Schlereth and Ryan Perry. But injury concerns dropped him to the ninth round in the 2006 draft, where the Yankees selected him one spot after Boston took Ryan Kalish.
Just months after the draft, Melancon went under the knife, which caused him to sit out all of 2007. It was during that time he refined his motion. He shot through the Yankees' system, reaching Triple-A in his first full season back. Like Bard, also a 2006 draftee, Melancon was groomed to pitch in relief. He hasn't started a game since college.
Blocked in New York, Melancon got a chance to close a lot sooner thanks to a 2010 trade to the Astros that featured Lance Berkman. By last May, Melancon took over as Houston's closer and never relinquished the job.
Will Melancon, once considered the heir to Mariano Rivera, instead take over for Papelbon?
As the roster stands now, Melancon appears to be the answer. However, there's still a great deal up in the air.
Daniel Bard: Starter or reliever?
As closers go, Bard has a far more typical repertoire than Melancon. His average fastball speed of 97.2 mph was the fourth-fastest in the majors.
His elite stuff is also why he's an attractive option for the rotation. On Saturday, Bobby Valentine indicated that Bard would be prepped as a starter and a determination on his role will be made in March.
Fastest Average Fastball (2011)
Henry Rodriguez, Nationals
Aroldis Chapman, Reds
Jordan Walden, Angels
Daniel Bard, Red Sox
Bobby Parnell, Mets
Bard has made 192 major-league appearances, but hasn't started a game since 2007 in Class A Lancaster. The only active pitchers with more relief appearances before making a start are Tony Pena (285) and Kyle McClellan (202), according to the Elias Sports Bureau.
A similar move to the rotation is nearly unprecedented in franchise history. Dennis Lamp made 128 appearances in a Red Sox uniform before making his first start, but he had started games earlier in his career. For a player that started his career with the Red Sox, Tom Bolton's 57 relief appearances are the most before making a start.
Questions remain about how Bard's powerful repertoire would fare in the rotation. The best precedent for Bard's potential transition is the Rangers' Alexi Ogando.
Most Relief Appearances for Red Sox Before First Start
Source: Elias Sports Bureau
Despite making only three starts as a minor leaguer and none in the majors, Ogando was moved into the Texas rotation in 2011. Like Bard, he'd excelled as a setup man, posting a 1.30 ERA in 44 appearances in 2010.
The experiment was a success. Ogando made the All-Star team and finished 13-8 with a 3.51 ERA.
Like Bard, Ogando has an overpowering fastball. In 2010, it averaged 96.2 mph and topped out in triple digits. So how much velocity did he have to sacrifice as a starter? Not too much. Ogando's fastball averaged 95.0 mph in 2011, reaching as high as 99.4.
Ogando had never pitched more than 75 innings in a season, and that showed late in the season. He posted a 7.14 ERA in six August starts, ultimately moving to the bullpen down the stretch.
As successful as Ogando was in the rotation, the Rangers missed his value as a reliable eighth-inning presence, which led them to make in-season trades for Mike Adams and Koji Uehara.
Who else might close?
If Bard does move to the rotation, the Red Sox need to fill openings in both the eighth and ninth innings.
Melancon clearly steps into one of those roles. Given his inexperience, the eighth is a far safer choice, at least in the short term.
Bobby Jenks has excelled in the closer's role in the past, but it's unclear how much Boston can count on him following an injury-plagued 2011. Like Bard, Alfredo Aceves figures to get a look in the rotation.
Boston still has significant external options to consider.
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While the top free-agent starters are off the board, several closers remain. The Marlins (Bell) and Phillies (Papelbon) filled their respective voids with big names. The Mets, Blue Jays, Padres, Rangers and Twins all found closers, while eschewing the remaining big names.
The number of teams looking for a closer thinned out so much that Francisco Rodriguez opted to accept arbitration, knowing he won't close in Milwaukee.
That leaves Ryan Madson, a closer without a home.
Stepping into the closer role for the Phillies, he posted 32 saves with a 2.37 ERA in 2011. Amazingly, Madson only allowed eight extra-base hits. By comparison, Papelbon gave up 15. But much like Rafael Soriano last offseason, Madson has fallen through the cracks despite a career year.
The Red Sox appear to be the most logical destination if he wants to close, and they want to pay him. Some reports point to the Angels as a potential suitor if they determine Jordan Walden needs more seasoning. Beyond that, most teams have already filled the role or don't seem willing to spend the money.
It remains to be seen if Ben Cherington is willing to spend big bucks for Madson. The odds likely increased once it became clear he wouldn't require draft picks as compensation. But other, less expensive options could be deemed more attractive.
Francisco Cordero and Brad Lidge, both proven closers, remain available, but understandably so. With 43 saves and a 2.45 ERA, Cordero's numbers appear ideal. But he's almost 37 with a rapidly declining strikeout rate. Meanwhile, Lidge hasn't been able to overcome health and control problems in the past three seasons.
As the Red Sox crafted the trade for Melancon, rumors swirled around A's closer Andrew Bailey. Boston lost two key trade chips in Lowrie and Weiland, but still could pursue Bailey. He's one of four pitchers with 24 or more saves in each of his first three seasons.
Jeremy Lundblad is a senior researcher with ESPN Stats & Information. He provides statistical analysis for ESPNBoston.com.