While Martinez is one of the top hitters in baseball he’s not necessarily among the best players. There are other aspects of the game beyond smacking the ball out of the park.
Defense is a key aspect as well, which is an area that Martinez is deficient in. His -5 defensive runs saved ranked 40th out of 56 qualified outfielders and his -14.8 UZR/150 was dead last. He also lacks a strong throwing arm to prevent runners from advancing, with a -7.7 ARM rating that ranked ahead of only two other MLB outfielders.
Martinez is best suited as a designated hitter, especially on a Red Sox team that is already loaded in the outfield. He’s obviously not moving Mookie Betts out of right field, the position which Martinez has primarily played throughout his career. He’s capable of playing left field but Andrew Benintendi isn’t going anywhere either. There have been rumors that Jackie Bradley could be moved this winter for a more consistent hitter. While Benny could conceivably move to center field to allow Martinez to take his spot in left, this scenario would result in a drastic defensive decline at two positions.
Baserunning is another area where Martinez struggles. He’s essentially a non-factor as a base stealer, with his career-high of six coming four years ago. Martinez also posted a dismal -5.7 BsR, FanGraph’s all-encompassing baserunning statistic, that ranked outside the top 200 in the majors (minimum 400 plate appearances).
As great as Martinez is at the plate, his flaws in other areas of the game drag down his value. No wonder his 3.8 fWAR placed him only 44th among major league hitters. Since 2014, Martinez has compiled a 14.6 fWAR that ties him for 34th in the majors among hitters over that span.
I would be remiss not to mention the health concerns that come with Martinez. He missed the first few weeks of this season with a sprained foot and ended up appearing in only 119 games. He’s played in more than 123 games only once in his career – in 2015 when he made his only All-Star appearance.