The best hitter you know nothing about

As every St. Louis fan knows, the Cardinals had an unexpected breakout season from a power-hitting righty outfielder in 2017. This is a player who was born in 1988, entered the professional ranks in 2006 and put up impressive stats at several levels of the Minors around a variety of injuries, finally managing to stick in the bigs in the year he turned 29.
You're probably thinking of Tommy Pham, because every word of that applies to St. Louis' starting center fielder. But it also applies to José Martínez, who very quietly put up a .309/.379/.518 line in 307 plate appearances last year. Like Pham, a big question entering 2018 will be whether Martinez can repeat his performance, whether '17 was a small-sample-size fluke. Unlike Pham, Martinez doesn't have a clear path to playing time.
Let's start with the important part, about whether a few hundred good plate appearances from a guy who turns 30 in July should be written off as a fluke or a beginning. After all, the Cards have seen a few hitters have splashy first impressions in recent years only to find that long-term success didn't follow, like with Aledmys Díaz and Jeremy Hazelbaker. Pham falls into that category in 2018; so does shortstop Paul DeJong.
So, of course, does Martinez. But while 2017 may have been his first taste of big league success, there's plenty of reason to consider him a reasonable bet to produce again in '18. For example, let's start with the fact that the numbers he put up in '17 didn't come by accident or good fortune. They were earned, and then some. In a partial season, Martinez's command of the plate ranked with the elite hitters in the game.

Here around the Statcast™ lab, we have an extremely powerful metric with a funny-sounding name. It's called Expected wOBA, or xwOBA, and it's intended to show total command of what the batter can do at the plate. It accounts for quality of contact, in terms of exit velocity and launch angle, and amount of contact, in terms of strikeouts and walks. It doesn't look at play outcomes, because the point is that a hitter ought to be credited for the skill shown in crushing a ball, regardless of whether a good defender catches it or a poor defender does not.
Expected wOBA leaders in 2017 (minimum 250 plate appearances)
.446 -- Aaron Judge
.424 -- Joey Votto
.423 -- Mike Trout
.423 -- J.D. Martinez
.411 -- Jose Martinez
.403 -- Freddie Freeman
(Major League average xwOBA is .314. Last season, 301 hitters had 250 plate appearances.)
What should stand out to you there is that the other names on the list are indisputably among the greatest slugging superstars in the game today. (More names in the Top 15: Giancarlo Stanton, Justin Turner, Carlos Correa and Bryce Harper.) If you look at the 2016 leaders, you'll see Miguel Cabrera, David Ortiz, Trout, Votto and Josh Donaldson. In '15, it was again Cabrera, Votto, Ortiz, Trout, Harper and Freeman.

The quality of the names alone should infer that being at the top of this list is a good thing. But just to be sure, let's take the Top 25 leaders (minimum 250 plate appearances) from each season in expected wOBA, and see how they did the next season in actual wOBA.
In 2015, of the Top 25 hitters in Expected wOBA, 22 went on to have above-average seasons in '16. Two who didn't, Mark Teixeira and Alex Rodriguez, were in their late 30s and playing their final season. One, Lucas Duda, got into only 47 games due to injury. Not everyone repeated their '15 success, but they were all better than league average.
In 2016, of the Top 25 hitters in Expected wOBA, 18 of the 23 who played went on to have above-average seasons the next year. (Two didn't play the next season.) Three of the five who didn't have good years were injured and in their mid-to-late 30s -- Cabrera, Albert Pujols and Victor Martinez.
It's fair to say that this guarantees nothing, and that Martinez didn't play a full season like most of these guys, but the point is that it is difficult to get there even in a partial season. Even if you just compare him to others who raked in less than a full year, Martinez (.411 xwOBA in 307 plate appearances) is right there with Rhys Hoskins (.399 in 212 plate appearances) and Matt Olson (.380 in 216 plate appearances).
So let's say this is "real." How did no one notice before now? Did the White Sox, Braves and Royals all whiff on Martinez for more than a decade before the Cardinals gave him a shot?
No. Mostly.
As usual, the story begins with health. By 2011, Martinez had been through three right knee surgeries, one costing him the entire '09 season. He was reportedly becoming the first player to make it back from a meniscus transplant. In addition, despite his 6-foot-6 height, Martinez had never hit for power, never once hitting double-digit homers until '15.

But that year, Martinez hit .384/.461/.563 in Triple-A, setting a Pacific Coast League record for batting average and leading the league in total value, per a Minor League version of WAR. When his 2016 season didn't live up to the same standard, he did something plenty of recent sluggers did before him: He studied the best hitters in the game and resolved to stop hitting ground balls.
"We started watching some swings from Donaldson and Cabrera, and we noticed that they don't hit ground balls," Martinez told local media during Spring Training. "They eliminate them."
It's a familiar story. Martinez showed elite exit velocity (his 90.6 mph average was in the top 20 in the Majors in 2017), and after years of hitting the ball on the ground over 50 percent of the time in the Minors, he cut his grounder rate to only 42 percent last season.
So if the question is whether there's something real behind the breakout, there absolutely seems to be. The underlying data is real. The change in approach is real. The remaining question is whether Martinez will get the playing time to prove it.
That's because even with Stephen Piscotty off to Oakland and Magneuris Sierra to Miami andRandal Grichuk to Toronto, the Cards have plenty of competition. Pham is set in center, with Marcell Ozuna and Dexter Fowler as the clear starters in the corners. Prospects Harrison Bader and Tyler O'Neill are ready now, and Jose Adolis Garcia may not be far behind. Rookie first baseman Luke Voit has been taking some outfield reps this offseason, too.
At first base, where Martinez is working to gain experience, there is, of course, still Matt Carpenter and Voit -- and never-ending rumors about Eric Hosmer.
Having too much talent is never a serious problem to have. These things tend to sort themselves out. Yet despite his winding path to the big leagues and his impending 30th birthday, it certainly looks like the skills behind Martinez's partial-season breakout were real. It's up to the Cardinals to give him a path to prove they were.