Center fielder Denard Span only made 275 plate appearances in 61 games for the Washington Nationals in the 2015 season. That's the big knock on him as he enters free agency for the first time in his career—without a qualifying offer. When he played this year, he hit .301/.365/.431 with a 120 wRC+.
Drafted by the Minnesota Twins in the first round of the 2002 amateur draft with the 20th overall pick, Span made his major league debut in 2008. In eight seasons in the big leagues, he has hit .287/.352/.395 with a 106 wRC+ while playing center field, aside from brief stints in the corner outfield spots with the Twins early in his career. He has stolen 152 bases in 193 attempts, a reasonable success rate of 78 percent, with his peak stolen base total of 31 coming in 2014.
Span will turn 32 years old before the 2016 season starts. A left-handed hitter, Span has been better against right-handed pitching than left-handed pitching in his career. He's hit .293/.353/.407 against righties, and if the Mets are looking for a platoon partner for Juan Lagares, who is a right-handed hitter and struggles mightily against right-handed pitching, Span looks like a pretty good option on paper.
But Span dealt with back issues for most of the season and spent a lot of time on the disabled list as a result. He first hit the DL in early July and only came back for two games in late August before missing the rest of the season. He obviously has all winter to get his back right, but it has to be at least a little bit of a concern for any team that might want to sign him.
The crowd-sourced projections at Fangraphs have span getting something like a three-year, $36 million contract this winter. If the upper end of the Mets' 2016 Opening Day payroll is hypothetically $115 million, that sort of contract for Span would account for about half of the $23 million difference between the team's existing commitments and that maximum. If the limit is lower than that, or if Daniel Murphy were to accept his qualifying offer, $12 million for Span would bring the Mets right up to or over that number.