Spring training results are basically meaningless, and yet as portents of things to come are concerned, Ketel Marte homering on Sunday, in his first plate appearance of the Cactus League season, was a positive. The 26-year-old Diamondback is coming off a breakout, MVP-caliber season, albeit one that ended with him on the sidelines. Marte didn’t play a single game after September 17 due to a stress reaction in his lower back, and while he didn’t need surgery, his recovery was something of an abstraction until that first knock; the same can be said for baseball in general.

Behold, let the new season begin:

Primer turno y primer jonrón para Ketel Marte. ? #MLBDominicana ?? pic.twitter.com/CJVoZGevEx — MLB Dominicana (@MLBDominicana) February 23, 2020

The switch-hitting Marte enjoyed a dazzling 2019, setting career highs in virtually every key offensive category. He hit .329/.389/.592, numbers that respectively ranked second, seventh, and fourth in the NL; his 150 wRC+ ranked fourth as well, behind only Christian Yelich (174), Cody Bellinger (162), and Anthony Rendon (154). That performance wasn’t anything that could have been expected given his previous history, as he entered the season a career .263/.324/.389 hitter, one fresh off a modest .260/.332/.437 (106 wRC+) showing in 2018. Marte’s 32 homers more than doubled his previous total of 22, compiled in over 1,500 plate appearances from 2015-18.

Marte’s season was all the more remarkable given that he split his time between second base and center field, the latter of which was virtually uncharted territory, as the totality of his previous professional experience there amounted to 95 innings, including 15 at the major league level with the Mariners in 2015. With general manager Mike Hazen unable to come up with a suitable replacement for departed free agent A.J. Pollock, Marte made 89 starts in the middle pasture, plus another 45 at second base, and five at shortstop; often, he switched positions mid-game, most commonly moving from center field to second base in the later innings. He played the new position particularly well, according to both UZR (+5.6) and DRS (+6), while he was a whisker below average at second (-1.3 UZR, -1 DRS).

Between that and his outstanding baserunning (4.2 runs by our metrics, though he went just 10-for-12 in steals), he finished with 7.1 WAR, ranking third behind Yelich and Bellinger (7.8 apiece), though Rendon (7.0) snuck ahead of him in the NL MVP voting. Needless to say, his performance was well ahead of his respectable 2018 showing (2.6 WAR), and in fact, he had the second-largest year-to-year gain in that category among players with at least 300 plate appearances in each season:

Likewise, Marte’s 45-point year-to-year gain in wRC+ ranked fourth.

In Monday’s chat, a reader asked me whether I thought Marte could repeat last year’s success. The question lingered in my mind long enough to set off my own investigation into his big surge.

From an offensive standpoint, Marte showed improvement in several different aspects of his game. In general, he hit the ball harder and in the air more frequently, a recipe that has spelled success for countless hitters of late, and for the first time since his abbreviated 2015 rookie season, he hit well against righties.

Ketel Marte’s Batted Ball Profile, 2018-19 Years GB/FB GB% FB% EV LA wOBA xwOBA 2018 Tot 1.77 51.2% 29.0% 88.5 5.7 .330 .320 2018 Tot 1.24 43.1% 34.8% 89.8 11.5 .405 .370 2018 LHB 1.70 50.5% 29.8% 87.0 5.8 .285 .298 2019 LHB 1.28 44.5% 34.8% 88.7 11.6 .411 .370 2018 RHB 1.89 52.4% 27.7% 91.0 5.6 .408 .369 2019 RHB 1.14 39.6% 34.7% 92.3 11.1 .406 .370 SOURCE: Baseball Savant

The pattern is fairly similar in terms of his year-to-year changes for left- and right-handed batting, but he went from a massive platoon split — in which he was rather anemic versus right-handed pitching — to a minimal one. Here’s a year-to-year comparison of his exit velocity by handedness and zone, first as a lefty hitter:

Marte hit balls in the mid-to-outer and mid-to-lower areas considerably harder, gaining around 7 mph of exit velo in those outer areas. Meanwhile, he actually took a significant step back against middle-middle balls from the right-hand side but produced far more oomph in the lower third of the zone, as well as the outer middle.

Here’s how it shook out, performance-wise:

Ketel Marte’s Platoon Splits, 2018-19 Year PA AVG OBP SLG wRC+ Pull Pull FB 2018 LHB 368 .224 .300 .352 75 33.1% 3.3% 2019 LHB 453 .328 .397 .578 150 41.9% 8.2% 2018 RHB 212 .321 .387 .584 158 42.8% 6.1% 2019 RHB 175 .331 .366 .627 151 47.9% 12.0%

As you can see, Marte was actually quite good batting right-handed in 2018, just as he was in 2019, but in the other 63% of his plate appearances, he was lousy. He shored that up in a big way, and among other things, pulled the ball with greater consistency, basically doubling his rate of pulled fly balls from either side of the plate. He hit 20 homers batting lefty, of which nine were pulled.

What’s odd — and what made me nearly go blind while playing with the splits tool, since all this lefty-righty stuff gets confusing when you’re going back and forth between website, spreadsheet, and writing — is that from 2015-17, Marte was utterly dreadful batting righty (70 wRC+ in 339 PA) but competent batting lefty (93 wRC+ in 629 PA). All of which is a good reminder that we’re still dealing with some small sample sizes in a young player whose growth has been rather uneven; recall that he spent the first half of 2017, his first season in the Diamondbacks’ organization, at Triple-A Reno after spending most of 2016 with the Mariners.

Per the Athletic’s Zach Buchanan, with the help of new hitting coach Darnell Coles, Marte’s breakout was fueled by a couple of adjustments in his left-handed swing, including a leg kick to help with his timing and a lower starting position for his hands. The results were convincing, to say the least.

With the recent acquisition of center fielder Starling Marte and the free agent departure of second baseman Wilmer Flores, the Diamondbacks plan to not only to party hearty but to do so by playing K. Marte at the keystone with more regularity. As I noted in the context of the trade with the Pirates, the team felt that the stress reaction that felled their versatile star was linked to the extra running he did in the outfield, and both Hazen and Marte himself suggested that Chase field’s new artificial turf may have been a contributing factor (though each downplayed that almost as soon as they brought it up). Hence the move back to second, where Marte has been basically average (-0.3 UZR/150 in almost 1,500 innings) for his career.

Given that the small-sample metrics suggest Marte was above-average in about half a season of work in center field, replicating last year’s 7.1 WAR becomes an even taller task, though it’s not as if regression is out of the question on that front anyway. Per our depth charts, Marte is forecast to produce 4.3 WAR this year, a step down from 2019 but still a very respectable contribution. To get some historical sense of what his chances are of being significantly more valuable than that, I took a look at players from 1995 onward who were worth at least 4.0 WAR in their age-25 seasons, then charted what they did at age 26. Excluding Marte and the four other players from 2019 who fit that bill (Alex Bregman, Francisco Lindor, Paul DeJong and Jorge Polanco), that left 83 players to compare:

Age 25 to Age 26 Drop-Off Range # Avg WAR 25 Avg WAR 26 Change 7.0+ 15 8.1 5.0 -38.3% 6.0-6.9 16 6.4 5.3 -17.4% 5.0- 5.9 18 5.4 3.9 -27.4% 4.0- 4.9 34 4.3 3.8 -12.7% 6.0+ 31 7.2 5.1 -28.7% 4.0-5.9 52 4.7 3.8 -18.5%

Not surprisingly, the most productive players at age 25 had the hardest time replicating their performances at 26, collectively experiencing a steeper dropoff, but for a seven-win player, that still amounted to a five-win follow-up, roughly speaking. For the players within half a win of Marte’s 2019 showing in either direction, the drop was a bit steeper, but this is still impressive company:

That’s two Hall of Famers with a third (Trout) on the way, and while there were some falls from grace, from among those, players such as Bryant, Ramirez, Wright, and Zimmerman still went on to produce seasons worth at least 4.0 WAR down the road.

While a true projection system that takes the components of each player’s performance across a multi-year period into account is a better way to go, this quick-and-dirty study underscores just how hard it is to replicate a season of the caliber that Marte just posted. It’s quite possible we’ve just seen his career year, a performance that he’ll never top, but recent history tells us there’s a reasonable chance that he’ll remain a star-level player for the foreseeable future.