Take a look at any Mets prospect list from 2017 and Amed Rosario was the headliner. He was all fast-twitch muscles and gorgeous defense. His frame was the type that looks perfectly suited for shortstop: tall and rangy, but not so lanky that he couldn’t one day hit for power. We saw him as a 65 FV prospect, the third-best in all of baseball.

After 2017 and 2018, that assessment looked sorely misguided. Over 762 plate appearances across those two seasons, he put up every scary number imaginable. He walked only 4.2% of the time while striking out 22% of the time, both worse than he’d performed in any full minor league season. Pitchers knocked the bat out of his hands; he hit for a .129 ISO despite 12 triples. The speed that made those triples possible didn’t translate into extra value; his BABIP was only .318, which is good but not great, and he was caught stealing a brutal 14 times.

Those are just offensive outputs, but the offensive and defensive approach were perhaps even scarier. He swung at 42% of pitches outside of the zone, the sixth-highest chase rate in the bigs. Every hitter who chased more often than him, however, channeled their aggression better; he somehow swung at a below-average percent of pitches over the heart of the strike zone in 2018 despite all the chasing.

On defense, his toolsy profile somehow didn’t translate at the major league level. His range was mostly as advertised, but the game looked quick when he was involved in the play. He was throwing without coming set, trying to field and plant in one motion, and generally attempting two actions in the time it takes to complete one. It showed in the results. Statcast’s OAA pegged him as the worst defensive shortstop in baseball. He was worth 11 outs below average when moving forward, a direction where most shortstops excel.

Of course, this being an article about Amed Rosario, you can probably guess what happened in 2019. His bat came alive, relatively speaking, to the tune of a 100 wRC+. He cleaned up his defense — depending on which metric you prefer, he got better by six runs (DRS), 4.4 runs (UZR), or four outs (OAA).



I’m just going to gloss over the defensive improvements quickly. Trouble coming in? Rosario stood three feet closer to home plate in 2019 than he did in his previous two seasons. That’s a big move — he went from roughly average to being the third-closest regular shortstop, with only Corey Seager and Adalberto Mondesi standing closer on average. OAA rated his defense coming in as average last year, a big improvement. He gave some of that back in lost value moving right, as he had less time to react, but it seems that the Mets are thinking about this the right way.

Rosario’s offense, like his defense, benefited from a change in approach. If “stand closer” is easy-to-digest advice, “pick a zone and swing there” is even more straightforward. Rosario has no trouble swinging, as we’ve already covered. But in 2018, he wasn’t consistent in where he swung. When he saw a fastball, he was looking everywhere, from middle-up to down and in:



That might not look surprising, but even free-swinging batters need a target. Javier Báez, the freest swinger in baseball, knows where he’s looking for a fastball:

It doesn’t mean he doesn’t swing at bad pitches, of course. But narrowing focus is a good way to get more swings at the places where you feel most comfortable. Rosario improved there in 2019. It doesn’t jump off the page, but he focused more on a single hot spot rather than dividing his swings evenly across multiple zones:

He accomplished a rare trick: he swung more at pitches over the heart of the plate, finally getting to above average there after his earlier timidity, while swinging less at pitches on the edges and outside of the strike zone. Some of that was the aforementioned fastball targeting, but he also made a significant second adjustment: He started swinging less at offspeed and breaking pitches:

Swing Rates by Pitch Type Year Fastballs Breaking Balls Offspeed 2018 51.7% 54.8% 61.7% 2019 51.4% 51.5% 53.3%

That’s another short teaching statement: “swing less at bendy pitches.” It’s easier said than done, however. Of the 54 batters who saw at least 1,000 non-fastballs in both 2018 and 2019, Rosario’s 4.2-percentage-point decrease in swing rate was the third-lowest. His nearly-unchanged fastball swing rate was in the middle of the pack. Xander Bogaerts did a clearly better job, swinging at 4.7% (percentage points) fewer breaking balls and 0.4% more fastballs, but no other batter combined Rosario’s improved ability to lay off secondaries with continued aggression on fastballs.

These two changes, targeting a fastball zone and laying off secondary offerings, unlocked the offensive game he was always capable of. If you’ll excuse me an arcane combination of letters, Rosario’s xwOBACON, which measures what production you’d expect on contact based on the speed and angle of his batted balls, has crept up slowly in each zone over the course of his career:

(x)Production on Contact by Zone Year Heart Shadow Chase 2017 .364 .319 .321 2018 .386 .328 .218 2019 .432 .339 .278

What does this mean? Essentially, he hasn’t unlocked some phenomenal cosmic power, sneakily transforming into Joey Gallo while we think he’s still a wisp-thin bundle of wire out there. He’s always had decent bat-to-ball skills; he’s merely wasted them with his swing selection. He’s gotten a little better over the heart of the plate, yes. But he’s also improved by putting more of those balls over the heart of the plate into play; he had 34 more in 2019 than 2018 and seven fewer in the chase zone.

This analysis is at risk of becoming more or less number soup, so here’s the bottom line: Rosario’s plate discipline improved from 2018 to 2019, which gave him a nice base to work from. If he replicated his 2018 season in non-contact events every year (excluding intentional walks), he’d need almost exactly average production on contact to be an average hitter overall. If he instead replicated his 2019 season, he could be 2% below average and still have the total package work out.

At the same time, he’s become a better hitter on contact, both by getting better in each zone and by more frequently swinging at fastballs in good locations. His 100 wRC+ doesn’t look like a one-off; he got through there by doing many little things right rather than with one huge fluky improvement. He’s swinging more at good pitches, less at bad pitches, and reaping the rewards. It’s a heartwarming story.

Of course, another take on this story is that his early struggles and later improvement aren’t particularly surprising. Take a look at his Steamer projections in a few rate stats since 2017:

Steamer Rate Projections by Year Year BA OBP SLB wOBA 2017 .245 .288 .337 .272 2018 .257 .296 .374 .288 2019 .262 .305 .391 .299 2020 .276 .318 .424 .313

Steamer wasn’t overly surprised by Rosario’s improvement. In fact, it projected him to be worse in both 2017 and 2018 than he actually was. It sees continued gradual improvement this year as well, taking 2019 with a grain of salt, but that projected line still works out to a 96 wRC+, which would make him an above-average regular at shortstop.

Maybe the story wasn’t that Rosario struggled to start his career — on offense, at least. Maybe the story is that expecting someone who played the entirety of the 2017 season at 21 years old to hit the ground running in the big leagues was always too optimistic. Not every prospect is Juan Soto or Mike Trout; outside of magical Christmas land, sometimes you just need a few years to mature and acclimate.

This will be Rosario’s third full season in the majors. He’ll be four years younger than the average major leaguer, which continues a theme; the only time in his entire pro career where he’s been less than three years younger than the league average was High-A St. Lucie in 2016, and he hit .309/.359/.442 there in 290 PA before the Mets promoted him to Double-A.

Amed Rosario projects to be an average regular in 2020 with the potential for more. That probably feels like a story of redemption to Mets fans, who have been waiting for this breakout since Matt Harvey was still a going concern. But really, it’s not. It’s simply par for the course for a talented young player who was so good in the minor leagues that he burst onto the scene at a precocious age.