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Fernando Tatís Jr. Was Already Mashing. Then He Started Hitting The Ball Harder.

Fernando Tatís Jr.’s grand slam on Monday got the debate going again about baseball’s unwritten rules, but there’s no debating the talent of the San Diego Padres shortstop. The 21-year-old entered play Friday tied for first in the majors in wins above replacement,1 making the Padres’ deal to acquire him look like one of the most lopsided in recent history.

Tatís has long been regarded as one of the top prospects in the game thanks to his rare set of physical tools, including elite speed and arm strength. But the phenom has been propelled to stardom by how quickly his ability to hit — and hit for power — has come together. Before amassing even 500 plate appearances in the majors, he is leading the league in home runs, RBIs and steals.2 And what should excite the Padres and their fans even more, and terrify the rest of the National League West, is how much Tatís has already improved.

In about half a season last year as a rookie, Tatís hit 22 home runs and stole 16 bases to go along with a .317 batting average. He posted a mark of 150 weighted runs created plus (wRC+), a metric that adjusts for annual ballpark factors and run environment, with an average of 100. That meant he was 50 percent better than a MLB-average hitter at just 20 years old, one of the youngest players in the majors. This season, incredibly, he’s been even better, boasting a wRC+ of 188 in 27 games. And his underlying skills also seem to be improving.

Tatís is second in the majors in exit velocity, or the speed at which the ball leaves his bat, at 96.3 mph. Among all qualified3 hitters this season through Tuesday’s games who had at least 300 plate appearances last season, Tatís was tied for the greatest improvement in exit velocity year over year. Along with his power surge, and perhaps contributing to it, Tatís has also become more selective about the pitches he swings at. He has reduced his out-of-zone swing rate by 8.1 percentage points — the 10th best improvement among 142 qualifying hitters through games Tuesday.

Tatís has cut down on swings against low-and-away breaking balls, a common chase area for batters, as seen by comparing a heat map from last season with this season. The improved discipline has helped him get ahead in the count 31.5 percent of the time this season, versus a 29.2 mark last season. And when he’s ahead in the count, he’s posted a 1.051 slugging mark. The improvement has resulted in shots like this:

All judgments in this unusual season are being made on small sample sizes. But to date in his young career, Tatís has been 59 percent more offensively efficient than the average hitter. That ranks him first all time in such production from shortstops age 23 and younger. While the premium, up-the-middle position has become more offensive-minded over the years — with roughly league-average wRC+ marks over the past two seasons — Tatís still stands out as an offensive force.

Given where he falls on aging curves, his prospect pedigree and the success of sons of former major leaguers,4 there are many indicators that suggest Tatís will have staying power as one of the game’s top players. With any luck, he’ll be rewriting baseball’s unwritten rules — and the standard for shortstop play — for years to come.

Check out our latest MLB predictions.

Footnotes

  1. According to FanGraphs’ version of the metric.

  2. He’s tied with four other players at six steals.

  3. Minimum of 3.1 plate appearances per team game.

  4. His father, Fernando Tatís, had an 11-year career in the majors.

Travis Sawchik is a sportswriter for FiveThirtyEight.

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