The 2017 Winter Meetings were a bountiful time for relief pitchers, but we've yet to see much movement among free-agent outfielders -- though Giancarlo Stanton and Marcell Ozuna changed teams via trade.
As a result, plenty of outfield talent remains. Below is a look at some of the most prominent outfielders on this year's market in terms of why teams would pay for them and why they could hesitate to sign the dotted line.
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J.D. Martinez

Selling point: Martinez is a poster example for baseball's air-ball revolution, and lifting the ball paid huge dividends last year. The right fielder struck a barrel, Statcast™'s term for balls in play with optimal combinations of exit velocity and launch angle), in 12.3 percent of his total plate appearances in 2017, a rate that was topped only by Aaron Judge. Only three players in baseball -- Stanton, Michael Trout and Joey Votto -- have accumulated at least 2,000 plate appearances and recorded a higher league-adjusted OPS+ than Martinez since 2014. The Red Sox are the closest-linked team to Martinez, and he could be the power bat that elevates a club that finished last in the American League in home runs.
Disclaimer: Martinez, 30, posted an average sprint speed of 26.8 feet per second in 2017 that came in just under the MLB average of 27. Martinez's sprint speed has declined in each of the last two seasons and figures to continue to do so with age, and his minus-5 Outs Above Average (OAA, Statcast™'s cumulative figure for all individual catch probability plays over a given season, explained here) ranked among the worst outfielders in the game. The right-field grass in both Fenway Park and AT&T Park, home of another rumored suitor in the Giants, features rather tricky dimensions that could test Martinez's range.
Jay Bruce

Selling point: Bruce, who's topped the 30-homer mark in each of the last two years, has become one of the most adept at lifting the ball. Bruce's 55.1 percent rate of batted balls hit with launch angles between 10 and 49 degrees (i.e. line drives and fly balls that cause the most damage at the plate) was topped only by Votto, Justin Turner and Kyle Seager last year among the 100 MLB hitters who put at least 400 balls in play. Bruce's left-handed power has reportedly piqued the interest of fringe contenders like the Blue Jays and Rockies.

Disclaimer: Bruce exceeded expectations as a right fielder last year but still came in with a slightly below-average minus-1 OAA rating, per Statcast™. His sprint speed last year was below average at 26.5 ft/sec, and he tends to see lots of shifts batting from the left side. The Giants are thought to have Bruce high on their wish list, but like Martinez the spacious right field in San Francisco could be tough for him -- or in Coors Field, for that matter. Neither Colorado nor San Francisco have the DH protection for Bruce in the National League.
Lorenzo Cain

Selling point: Numerous buyers in this year's market could stand to upgrade their center-field speed and defense, and no free agent is better positioned to do that than Cain. The rangy Cain's 29.2 ft/sec sprint speed tied for 16th fastest among Major Leaguers last year, and he ranked fifth on Statcast™'s OAA leaderboard at 15 Outs Above Average. Cain could go a long way in transforming the outfield of either the Blue Jays or the Giants, two reported interested parties who were the Majors' two worst clubs in team OAA last season. 
Disclaimer: The chief worry for Cain isn't connected to his past so much as his future. He turns 32 in April and his speed has arguably exceeded expectations already for his age, as we know that a player's speed starts to decline after age 28. The clear drop-off in sprint speed generally appears at age 33, and the expectation is that Cain will seek a four-year deal. 
Carlos Gonzalez

Selling point: Gonzalez is coming off his poorest full offensive season as a professional, but he's still generated plenty of interest from teams -- including the A's, Blue Jays, Giants, Orioles, Rays, Rockies and Royals. Shoulder issues were clearly hampering Gonzalez while he posted a .221/.299/.338 slash line over the first half of 2017, but teams appear willing to take a flyer and see if they can get the Gonzalez who hit .314/.390/.531 in the second half. The veteran was a top-35 player in terms of Statcast™'s hard-hit rate (or rate of batted balls hit with exit velocities of at least 95 mph) in both 2015 and '16, and he ranked among the 20 best hitters in that regard over the second half of 2017.

Disclaimer: Though he picked up his performance down the stretch, Gonzalez's 2017 campaign on the whole could scare off teams -- especially given that he will be 32 on Opening Day. CarGo's splits away from Coors Field were also striking; he was a .323 hitter with a .923 OPS in 70 home games last year, as opposed to a .203 average and a .606 OPS everywhere else. 
Jonathan Jay
Selling point: Barring a forgettable 2015 season with the Cardinals, Jay has proven himself as a league-average hitter who gets on base enough to be penciled in at the top of a lineup. Jay keeps his strikeout totals low and hits well enough for average to set the table.
Disclaimer: The Mariners were an early player for Jay before they traded for Dee Gordon with the intention of moving Gordon to center field. Jay himself has expressed a desire to return to the Cubs, though Chicago is already overstocked with outfielders. Jay has ranked below average in each of the first two seasons of OAA, and his 26.6 ft/sec sprint speed in 2017 was both below the league average and among the slowest marks for center fielders.
Cameron Maybin

Selling point: The Royals are reportedly interested in Maybin as a potential replacement for Cain, and the center fielder would fit into Kansas City's style of play. Maybin's 33 steals in 2017 were his highest total since '11 with the Padres, and his 27.8 ft/sec sprint speed remains above league average. Maybin put a ball in play on 44.3 percent of his swings last year, a top-50 rate in baseball and right in line with the Royals' high-contact mantra.

Disclaimer: While Maybin's speed can help a team, his .228 average and .318 on-base percentage in 2017 leaves room for improvement. 
Carlos Gomez

Selling point: Gomez's 106 OPS+ was his best mark since 2014 with the Brewers, and he rebounded from a minus-5 OAA rating in '16 to a respectable plus-2 mark last season. Gomez was among the league's 100 fastest players at 28.1 ft/sec, even at age 31, and his arm is still borderline elite with a 93.2 mph average on max effort throws that tied for 10th best.
Disclaimer: Though he's retained much of his athleticism, Gomez still occupies the same space as Gonzalez: outfielders looking to recoup their market value in 2018. He's struck out in roughly 30 percent of his plate appearances over the last two seasons, a high mark for someone who is not an elite power hitter.
Melky Cabrera

Selling point: Cabrera still appears to have his bat-to-ball skill at the plate after he posted a 29.1 percent line-drive rate that ranked 10th best among MLB hitters with at least 400 balls in play, per Statcast™. Rockies second baseman DJ LeMahieu was the only qualified player in baseball who missed on a lower rate of swings than Cabrera last season (minimum 1,000 swings). He's a decent bet every year to hover near the .300 mark while knocking at least 30 doubles.
Video: DET@KC: Melky plates a pair with a single to right
Disclaimer: Cabrera's 26.1 ft/sec sprint speed was third worst among qualified right fielders last season, and he posted baseball's second-worst OAA.