In Joel Hanrahan and Brock Holt, the Red Sox  acquired a pitcher whom they consider an elite closer along with a middle infielder with a nice range of skills who serves as a solid complementary/depth option for the major league roster.
Hanrahan, 31, was an All-Star closer for the Pirates in the last two years, during which he recorded 76 saves (in 84 attempts, good for a 90.4 percent success rate) with a 2.24 ERA. During that time, opponents had just a .205 batting average against the right-hander, including a .187 mark in 2012.
While his walk rate spiked from 2.1 per nine innings in 2011 to 5.4 in 2012, the Sox — who scouted the right-hander heavily in September — did not see diminished stuff. His fastball remained a 96 mph offering, and his slider remained a wipeout pitch, capable of getting swings and misses in volume. Hanrahan did struggle with both command and results in the final month of the season, the Sox felt that hi struggles reflected the fact that he was pitching in uncompetitive situations, both because the Pirates had spiraled rapidly out of contention and because Hanrahan was pitching primarily in non-save situations, much as was the case when Jonathan Papelbon  pitched in non-save situations.
In a best-case scenario for the Sox, Hanrahan gives the team an elite closer who can help the team to create a deep bullpen, with Hanrahan the closer behind setup men Andrew Bailey , Junichi Tazawa and Koji Uehara (and, if he is not traded, Alfredo Aceves ), along with left-handed options Andrew Miller , Franklin Morales  and Craig Breslow , along with a wild card in Daniel Bard .
While the Sox had a relative wealth of talented arms last year, the absence and then struggles of Bailey and the inconsistency of Aceves resulted in a number of Sox losses in the late innings. The team was just 35 of 57 in save opportunities, a poor 61 percent conversion rate.
While Hanrahan is eligible for free agency after 2013, if he performs at an elite level, the Sox would consider making him a one-year qualifying offer either to bring him back to Boston on a short-term deal or in order to secure a draft pick if he signed elsewhere. (However, the limited market this winter for free agent Rafael Soriano  — caused in no small part by the fact that he would cost a signing team a draft pick — serves as a cautionary tale for the idea of draft pick compensation.)
Meanwhile, if the Sox struggle and are out of it at the trade deadline, the team anticipates that — so long as he is healthy and performing up to his abilities — he would have considerable trade value at the deadline. Alternately, Hanrahan would give the Sox greater flexibility to deal from a deep group of potential impact right-handers, either this offseason or during the year.
As for Holt, the Sox consider him a prospect, albeit a slightly older one at 24. He was selected by the Pirates as a senior out of Rice in the ninth round of the 2009 draft and has advanced steadily (despite a knee injury that cost him a considerable amount of 2010), reaching the big leagues at the end of 2012.
He’s a middle infielder who has played primarily shortstop in the minors but who is also capable of playing second. As a left-handed middle infielder, Holt fits a profile that can be hard to find (something reinforced by the $9.5 million deal for left-handed-hitter Stephen Drew ), with some useful skills that profile to average or slightly above.
In four minor league seasons, he’s hit .317/.381/.427/.808 with 11 homers and 49 steals. As those numbers would suggest, he has limited power and is more of a singles and doubles hitter who uses the whole field and can run well. He profiles as an above-average runner an good fielder who can also offer roster value as a defensive replacement and pinch-runner, while offering depth in case of injury at a number of positions. The Sox viewed him as someone who plays with terrific energy, a grinder who is all over the field. He also has three options remaining, making him a good roster depth option for multiple seasons.
In order to acquire the two players from the Pirates, the Sox gave up Mark Melancon , Stolmy Pimentel, Jerry Sands and Ivan De Jesus. Melancon, Pimentel and Sands all have interesting upside, and the Pirates could well benefit considerably from the deal. But while they were motivated to move one of their most expensive players (Hanrahan will likely earn in the vicinity of $7 million) to address other needs, the Sox were motivated to move players off the back end of their 40-man roster. The team was maxed out, with a need to create a roster spot for Stephen Drew and perhaps Mike Napoli  (or, of his deal falls apart, another first baseman).
In this deal, the Sox took three players who wouldn’t necessarily have fit on the opening day roster (and Melancon, notably, doesn’t have any options left), in exchange for an All-Star who’s been one of the better performers at his highly specialized position.
The Sox are well aware that Melancon — who was excellent in September — could excel and return to closer status in the NL Central, the division where he emerged as a standout reliever in 2011 with the Astros.
There is also belief that Pimentel’s three-pitch arsenal — a mid-90s fastball, a changeup that can be a strong swing-and-miss offering in stretches and a slider that has shown potential — could allow him to emerge as a soilid big leaguer, whether out of the bullpen or in the back of the rotation — but he’s developed slower than expected in his two years on the 40-man roster, never pitching above Double-A, and alternating outstanding stretches with struggles at that level in 2012. He’ll use his final option in 2013, and with the Sox’ 40-man roster at capacity, Pimentel represented the type of player whom it made sense for the Sox to move.
Sands is an intriguing player who showed big power in the minors, though with a high strikeout track record that created uncertainty about whether he could be more than a bench player offering depth at first and in the two outfield corners. He, too, was likely to open 2013 in the minors, as the acquisition of Jonny Gomes and presumed acquisition of Napoli rendered him redundant. If he can reach his considerable power potential, then the 25-year-old would represent a nice get for the Pirates, particularly given the dearth of power in the game right now. But, again, Sands is a more advanced but lower-ceiling player than other prospects in the Sox system such as Bryce Brentz.
De Jesus was a spare part, a backup utility infielder whose primary position is second base – less valuable than the more defensively versatile Pedro Ciriaco and than Holt, who is a better runner and defender than De Jesus. He was designated for assignment, cleared waivers and outrighted to the minors in November.
The Pirates did well to get a number of players who a) have plenty of control (Melancon won’t be eligible for free agency until after 2016, and Pimentel, Sands and De Jesus all have six full years of team control) and b) offer depth and potential at a number of positions for their big league club, while the Sox potentially come out well for having gotten trade value for an impact big leaguer at a time when they had to get rid of players on the 40-man roster. They got a pitcher in Hanrahan who now likely represents their bullpen anchor while doing little to impact their anticipated big league roster for 2013.