Napoli just one of several Red Sox free agents to earn their keep

Mike Napoli has been a good investment for Boston this season. (Jared Wickerham/Getty Images) Earlier this week, Mike Napoli spent his 165th day on the Red Sox

Mike Napoli has been a good investment for Boston this season. (Jared Wickerham/Getty Images)

Earlier this week, Mike Napoli spent his 165th day on the Red Sox roster, a threshold which triggered the maximum bonus payout in his one-year contract. Any way you slice it, the deal -- which is now worth $13 million -- has been a good one for both sides, one of a handful of free agent contracts that looked questionable at the time but have helped Boston rebound from last year's dismal last-place showing to compile the American League's best record despite trimming nearly $21 million off their Opening Day payroll from 2012 to 2013.

Back in December, the Sox agreed to a three-year, $39 million deal with Napoli, who had hit .227/.343/.469 with 24 homers for the Rangers in 2012 and spent five weeks on the disabled list due to a quad strain. When the 31-year-old slugger took his physical as part of the process of finalizing the deal, the team discovered that he had a degenerative condition in his hips. Napoli remained unsigned until Jan. 17, when general manager Ben Cherington and company reworked the agreement into a one-year, $5 million deal plus incentives for days on the roster and/or plate appearances. By reaching the 165th day, he earned the full bonus of $8 million, thus equaling the average annual value of his initial deal.

Napoli has been worth it even beyond his .258/.351/.478 line with 21 homers in 538 plate appearances. After catching 72 games last year, he's eschewed the tools of ignorance entirely in favor of becoming an everyday first baseman for the first time in his career — and a surprisingly good one. Various defensive metrics put him anywhere from four to nine runs above average in the field, while his previous numbers at the position had him average or a few runs below. All told, he's been worth 3.3 Wins Above Replacement according to Baseball-Reference.com's version of WAR, which uses his +9 Defensive Runs Saved as its defensive input. At a back-of-the envelope exchange rate of $5 million per win, that translates into $16 million worth of performance with about 10 percent of the season still to play.

Napoli was one of seven players the Sox signed to free-agent deals over the winter, only one of which was longer than two years. Here's a quick look at how the other six players — listed in order of the total size of their contracts — have fared.

Shane Victorino, RF (three years, $39 million)

Boston's largest deal was also its most criticized one (both here and elsewhere), primarily because the 32-year-old switch-hitter had shown major platoon issues in recent years, hitting .244/.311/.390 in 1,366 PA against righties from 2010-2012, and .229/.296/.333 in 472 PA in 2012 alone. Victorino has rebounded to hit a respectable .286/.344/.435 in 317 PA against righties, in part because oblique and hamstring injuries forced him to give up switch-hitting, at least temporarily. Batting righthanded against some righties after Aug. 4, he has been shockingly effective, hitting a searing .316/.409/.553 with five homers in 89 PA, compared to .275/.318/.391 with three homers in 228 PA while batting from the left side. Meanwhile, he's raked against lefties at a .302/.358/.484 clip in 175 PA. He's also stolen 20 bases in 23 attempts to go with his 14 homers, and his defensive numbers have been uniformly off the charts (+23 DRS, +23 UZR, + 20 Fielding Runs Above Average). All told, he's been worth 5.7 WAR, a performance worth around $28.5 million dollars, making the first year of his deal a massive win for Boston and going a long way toward justifying its entirety.

Ryan Dempster, SP (two years, $26.5 million)

As was the case in his late-2012 stint with the Rangers, the 36-year-old righty has struggled to keep the ball in the park (1.4 homers per nine) and has battled his control as well; his 4.1 walks per nine and 2.0 strikeout-to-walk ratio are his worst since moving back to the rotation in 2008, and not by a little. Though he does rank third on Boston's staff in innings (162 2/3), his 4.70 ERA is now the worst among Sox pitchers with more than six starts. All told, his performance has been 0.2 wins below replacement — so bad that it could be argued that instead of suspending him for his vigilantism against Alex Rodriguez, the bigger punishment would have been keeping him on schedule.

Jonny Gomes, LF (two years, $10 million)

Generally considered a part-timer due to his platoon-based struggles against righties, Gomes has started just 21 times against them this year compared to 50 times against lefties. Even so, his on-base and slugging percentages against pitchers of either hand are virtually identical despite a 50-point difference in batting average in favor of righties (.261/.331/.415 in 164 PA, compared to .211/.335/.415 in 175 PA against lefties) and 12 homers overall. Take his -20 DRS -- primarily in leftfield -- with a grain of salt; defensive metrics have long struggled to grapple with those playing in the shadow of the Green Monster, and besides, he's only at -4 UZR and -4 FRAA. His 0.8 WAR is almost right on the money given his annual salary of $5 million, and he may be a bit more valuable than that; via Baseball Prospectus' WARP he's been 1.2 wins above replacement.

Stephen Drew, SS (one year, $9.5 million)

A concussion delayed his regular season debut until April 10, and he finished that month hitting just .154/.267/.250, but the 30-year-old Drew is now up to a respectable .247/.330/.431 with 12 homers in 452 PA. Even with a subsequent three-week DL stint, he's seen more playing time than in any year since 2010. Despite his middling defense, Drew has been worth 2.3 WAR, a performance valued at about $1.5 million -- in other words, he's been worth the investment.

David Ross, C (two years, $6.2 million)

The Practically Perfect Backup Catcher has been limited to 32 games due to a concussion and ensuing complications that have forced him onto the DL for a total of 77 days spread over two stints. When available, the 36-year-old backstop has hit just .202/.290/.382, but he's thrown out 34 percent of would-be base thieves and allowed just one passed ball, providing enough defensive value to be worth 0.4 WAR. If that hasn't quite justified his $3.1 million salary, he's not far off, and hardly to blame for the circumstances which have shelved him.

Koji Uehara, RP (one year, $4.25 million)

Here's another huge win for the Sox. With Joel Hanrahan and Andrew Bailey both suffering season-ending injuries, Uehara moved from a setup role to closing duty in late June and has been lights out. He's put up a 1.08 ERA, 12.6 strikeouts per nine and a 10.3 strikeout-to-walk ratio in 66 2/3 innings overall, and has converted 18 of 20 save opportunities since taking over the ninth inning. What's more, he's retired his last 34 hitters dating back to Aug. 17, the equivalent of a perfect game plus 2 1/3 additional perfect innings. All told, the 38-year-old righty has been the AL's most valuable reliever at 3.4 WAR, worth about four times what the Red Sox are paying him.

David Ortiz

Jacoby Ellsbury

Dustin Pedroia

John Lackey

Clay Buchholz

Dodgers