Centerfielder/Sabermetric superstar Kevin Kiermaier signed an extension with the Tampa Bay Rays for 6/53.5M this week. Dave Cameron of FanGraphs notes that he will receive roughly 30M for three arbitration seasons and 12M per year for three free agency seasons. There will also likely be a 12M team option. Cameron’s article, while rightfully criticizing Major League Baseball’s flawed arbitration system, will run counter to my argument. Kiermaier is an excellent player, no doubt – a defensive wiz, great base runner, and a league average bat to boot. One thing that is not on his side is age. Kiermaier will be 27 this season, would have been 30 in free agency, and will be 33 or 34 when his contract is over. Much of Kiermaier’s value is derived from his defensive prowess; he has recorded a 44 UZR for his work in center field in his career. While this is impressive, the precedent for Kiermaier to continue this excellence through his free agent years is unlikely. Let’s consider the center fielders of the UZR era who have signed significant free agent contracts.

Major Free Agent Center Fielders’ UZR

Player FA Age Contract CF UZR (Pre-Contract) CF UZR (Post-Contract)
Carlos Beltran 28 7/119M 16.1 15.1
Juan Pierre 29 5/44M 32.6 -0.8
Gary Matthews Jr. 32 5/50M 12.4 -24.4
Torii Hunter 32 5/90M 11.9 -17.7
Aaron Rowand 30 5/60M 46.2 7
Melvin Upton Jr. 28 5/75.25M 18.6 1.6
Angel Pagan 31 4/40M -1.5 -25.6
Michael Bourn 30 4/48M 51.6 -14.2
Jacoby Ellsbury 30 7/153M 28.9 -2

*data via FanGraphs

Here we see a list of center fielders with (mostly) fantastic defensive records before signing a free agent contract around the age of 30. With the exception of Carlos Beltran, the youngest player on this list, every single one of these players’ defensive value in center cratered. All of them were or will be rendered unplayable in center before the expiration of their contracts. Kevin Kiermaier is a fantastic center fielder, but even he is no immortal among these men. With the stench of the Jacoby Ellsbury deal still fresh in the air, it is likely that most executives around the game will prefer developing defense rather than buying it.

The Rays get to pay Kiermaier 24-36M for 3-4 free agent seasons in exchange for the guaranteed money during his arbitration years, but if Kiermaier the hypothetical free agent isn’t going to be paid for his defense, is his bat really going to be worth 3/24M or 4/36M? Looking at Kiermaier’s place among center fielders with at least 1000 plate appearances in the previous three seasons, his wRC+ made him this red mark on the graph.

wRC+ chart

He’s holding his own (league average), and this is around where he has been for his whole career, but this is also supposed to be his prime. If this is the offensive peak (plateau?) of Kevin Kiermaier, it’s hard to imagine him creating 24-36M worth of value if the plateau crumbles around the age 30 mark.

While Kevin Kiermaier is a bonafide stud, it’s likely he will only be one until he reaches what would have been his free agent years. By signing this extension, I believe Kiermaier increased his career earnings, while taking that money guaranteed. However, don’t presume that Tampa was reckless about the 24-36M they will allocate to Kiermaier over those last three or four years; precedents can be broken, and he is an awesome player. It’s also important to consider the new asset that Tampa upgraded to, a nice Adam Eaton-esque carrot to dangle in front of interested teams – seven years of control of Kevin Kiermaier.