Like many other baseball players who grew up in Georgia, Jason Heyward was drafted by the Atlanta Braves. The team took him out of high school with the 14th overall pick in the 2007 amateur draft. Three years later, the highly-touted outfielder arrived in the big leagues, and he did not disappoint.
In his rookie season, at the age of 20, Heyward hit .277/.393/.456 with 18 home runs and a 134 wRC+ in 623 plate appearances and finished second in National League Rookie of the Year voting to Buster Posey. By wRC+, that is still the best season of Heyward's career as a hitter. He hit just .227/.319/.389 with a 96 wRC+, but he's been comfortably above league average in every season since then.
In 2012, Heyward hit what now looks like a fluky career-high 27 home runs, and he finsihed the year with a 121 wRC+. And over the next three seasons, he stayed right around that mark, finishing the last three seasons at 120, 110, and 121. Add it all up, and Heyward is a career .268/.353/.431 hitter with a 118 wRC+. In other words, he's a comfortably-above-average hitter, but he's not a spectacular one. And he has stolen twenty or more bases in three of his six major league seasons, a nice bonus but perhaps not an incredibly significant one.
But through his first six seasons in Major League Baseball, Heyward has been worth 27.8 fWAR and 31.1 bWAR, thanks in large part to his defensive play in right field. Heyward has won three Gold Glove awards at the position, and he's currently at a total of 119 Defensive Runs Saved and an 18.4 UZR/150 in right field. There might not be a consensus on the value and measurement of corner outfield defense in general, but Heyward seems to be among the very best at it.
Last November, with just one season left before Heyward hit free agency, the Braves sent the outfielder and relief pitcher Jordan Walden to the St. Louis Cardinals for starting pitcher Shelby Miller and minor league pitcher Tyrell Jenkins. Now, at 26 years old, Heyward is a free agent, considered by many the best position player player available on the market. The crowd-sourced contract projections at Fangraphs have Heyward getting, on average, an eight-year, $184 million contract this winter.
Given his age, such a contract wouldn't take on the risk of sharp decline or uselessness for a player being paid significant money in his late-30s. But there's at least some risk that either his bat or his defense will decline.
The Mets have two corner outfielders on their 2016 roster already in Curtis Granderson and Michael Conforto. Granderson is signed through the 2017 season, and Conforto's major league career has only just begun. If the Mets were to shock the baseball world and sign Heyward to a big contract—the odds of which seem very, very slim—they would have to play him or Granderson in center field regularly, at least until Granderson's contract expires.
Heyward has spent the grand majority of his major league career playing his regular position in right field, with 6,765.1 innings there and just 233 innings in center field. Yoenis Cespedes had played slightly more in center field when the Mets acquired him, but Heyward would present a similar situation: a very good corner outfielder manning center field as best as he can. With Juan Lagares signed through the next several seasons, the Mets could make late-game shifts to improve defense, as they did frequently after the trade deadline in 2015.
Of course, Heyward is probably a moot point for the Mets because of the money. But in the hypothetical scenario that they could afford such a player, he'd be a fascinating case given the Mets' needs and obvious opportunity to contend for at least the next couple of years.