With free agency underway, it's time to take a closer look at some of the biggest names available on the open market this offseason.
Among them is J.D. Martinez, who's arguably the top bat in this free-agent class. After a right foot injury delayed his season debut to mid-May, the 30-year-old outfielder hit .303/.376/.690 with 45 home runs in just 119 games with Detroit and Arizona.
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Here's a look at five Statcast™ metrics that help show why Martinez is one of the most attractive options in free agency:
1. xwOBA
Martinez was among the best hitters in the Majors in 2017, and it shows in his Statcast™ metrics. He finished the season ranked fourth in the Majors in expected weighted on-base average, or xwOBA, trailing only Aaron Judge, Joey Votto and Michael Trout (minimum of 400 at-bats). xwOBA combines a player's strikeouts, walks and quality of contact on batted balls to produce an all-encompassing offensive metric that removes the opposition's defense from the equation.
Highest xOBA in 2017 (minimum 400 at-bats)

1. Aaron Judge, .446
   
2. Joey Votto, .424
   
3. Mike Trout, .423
   4. J.D. Martinez, .423
   
4. Freddie Freeman, .403

2. Homer rate
Martinez provided a major spark for Arizona's offense upon joining the team via trade on July 18. He clubbed 29 home runs in 62 games, eclipsing Mark McGwire's MLB record (24 for St. Louis in 1997) for most homers hit by a player who was traded on or after July 1. While with the D-backs, Martinez homered on a remarkable 5.4 percent of his swings, the second-highest rate in that stretch (minimum 300 pitches swung at). Only 2017 home run leader Giancarlo Stanton homered at a higher rate (6.4 percent).
Highest rate of home runs/swings after July 19 (minimum 300 pitches swung at)

1. Giancarlo Stanton, 6.4 percent
   
2. J.D. Martinez, 5.4 percent
   
3. Josh Donaldson, 4.9 percent
   
4. Rhys Hoskins, 4.8 percent
   
5. Aaron Judge, 4.6 percent

3. Barrels
When Statcast™ was implemented in 2015, it allowed for the measurement of the quality of contact hitters make on batted balls, including exit velocity and launch angle. When a batted ball has an exit velocity and launch angle that typically yields a minimum .500 batting average and 1.500 slugging percentage, it's classified as a barrel. In the three seasons since Statcast™'s introduction, Martinez ranks second among all hitters in the number of barrels he's accumulated (182). He's 10 barrels shy of the leader, Seattle's Nelson Cruz, in that span, and Martinez led all Major League hitters with 74 in '15.
Most barrels since 2015

1. Nelson Cruz, 192
   2. J.D. Martinez, 182
   
2. Khris Davis, 174
   
3. Mike Trout, 172
   
4. Giancarlo Stanton, 165

4. Hard-hit and barrel rates
With the sheer amount of barrels produced by Martinez's bat, it's no surprise he was second in barrel rate last season at 19.5 percent (minimum 300 balls in play). Judge paced the big leagues with a 25.7-percent rate. Martinez also ranked among the Major League leaders in the rate at which he generated hard contact, which Statcast™ defines as a batted ball with an exit velocity of 95 mph or greater. The slugger ranked fifth in that category at 48.4 percent (minimum 300 balls in play).
Highest barrel rate in 2017 (minimum 300 batted balls)

1. Aaron Judge, 25.7 percent
   2. J.D. Martinez, 19.5 percent
   
2. Khris Davis, 17.7 percent
   
3. Giancarlo Stanton, 17.4 percent
   
4. Nelson Cruz, 14.2 percent
   Hard-hit rate in 2017 (minimum 300 batted balls)
   
5. Aaron Judge, 55.0 percent
   
6. Khris Davis, 52.1 percent
   
7. Nelson Cruz, 48.7 percent
   
8. Ryan Zimmerman, 48.6 percent
   5. J.D. Martinez, 48.4 percent

5. Slugging on pitchers 95 mph or greater
Martinez has not only excelled at making hard contact, he's also proven adept at hitting the highest-velocity pitching. He ranked first in baseball in slugging percentage on pitches of 95 mph or greater in 2017 (minimum 40 such at-bats). His 1.023 slugging percentage on those pitches is notably higher than the second-best mark, Jose Ramirez's .851.
Highest SLG on pitches 95 mph or greater in 2017 (minimum 40 at-bats)
1. J.D. Martinez, 1.023
2. Jose Ramirez, 0.851
3. Khris Davis, 0.797
4. Jose Martinez, .764
5. Yonder Alonso, .750