What is Didi Gregorius actually worth?

Consistency isn’t really something that’s attainable in baseball. A .300 hitter doesn’t hit .300 every month; he hits .200 in April, June and August, then .400 in May, July and September. The game is too prone to randomness to be able to pencil in anyone for “consistent” month-over-month production.

Nobody embodies that better than Didi Gregorius. Everyone knows by now the story of his 2018: the Ruthian April, followed by just about the worst May a professional baseball player could have. Since then he’s recovered and been a respectable hitter offensively, but just the visual of his year is mindblowing:

As Didi’s bat has come around, it got me thinking about his overall value as a player. Since becoming a full time player in 2015, he’s shown a remarkable ability to improve in each season. Offensively, at least, it’s easy to see why:

Most of Didi’s offensive production comes from his ability to get the ball in the air. Few players in baseball have benefited as much from the fly ball and launch angle revolutions, but interestingly enough he’s been bucking that trend for most of this season:

This refutation of the gradual, year-over-year trend above shows us a couple things. First, since Didi was so good at getting the ball up in May, and his hard contact rate was just 50 basis points lower than April’s, most of the month can be chalked up to rotten luck. As for his rebound, it’s possible that that’s a reversal of his fortune. He’s not generating as many fly balls but is still producing, indicating that this recent stretch of solid play may be good luck more than a display of skill.

Since stretches of good and bad luck tend to cancel each other out, we can probably assume that Didi’s 113 wRC+ is right about where he is as a true talent player. That’s a great mark for a shortstop, but it also shows that Didi is probably at his peak as a player. His rate of improvement has dropped pretty much every year:

This kind of year-over-year change is generally classified as increasing at a decreasing rate. The player is getting better each season, but getting less better each season than the previous. The decline in improvement generally matches up with a player’s peak or plateau, and then you begin to see a decline in production along a pretty standard ageing curve.

That Didi is at his plateau now is also reinforced by his projected rest-of-season totals. ZiPS and Steamer both project him to hit a little worse than he has this season for the rest of the year, and tag him to be worth between 4-4.2 fWAR for the full 2018. That’s a lot of value out of your shortstop, but Didi was worth 4.1 fWAR last season. There’s just not much improvement expected out of him.

All of this comes into focus because the Yankees have just one year left of control over Didi. He becomes a free agent after next season, after his age-29 season. If we’ve established that he’s probably at his peak now, it calls into question what kind of value the Yankees project for him as he enters his 30s. The time for an extension has probably passed, and both Didi and the Yankees’ camps are probably accepting that the shortstop will test the waters of free agency.

We’ve seen how the market for post-peak players has collapsed over the past few seasons. Teams just aren’t willing to lock up players unless they believe he’ll continue to improve over at least a chunk of a contract. If Didi is at his best right now, it casts a lot of doubt over what his future will look like as free agency approaches.