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Over the course of his career, Marcus Semien has been nothing if not consistent. It’s quite remarkable, really — the 28-year-old shortstop has posted between a 95 and 98 wRC+ in each of his three full seasons (and one half season) since being traded to the Oakland Athletics by the Chicago White Sox in 2014. He has long provided a modest blend of power and speed, and his well-documented defensive improvements last year boosted him to a career high 3.7 WAR and placed him squarely in the tier of not-great-but-pretty-darn-good shortstops in a league flush with some pretty darn good ones.

It may seem a bit strange, then, to suggest that such a player could be on the verge of a breakout, having already "broken out" last year and being on the wrong side of baseball’s aging curve. And yet, in the early weeks of the 2019 season, Marcus Semien appears to be suggesting that he is ready to do just that.

A bit of context: Semien has really flashed all the various facets of his potential at one time or another as he’s settled into a regular at shortstop for the A’s, but hasn’t quite managed to put together a season that has wrapped it all up. He knocked 27 home runs in 2016 (although there was little in his batted ball profile to suggest any sort of adjustment), has consistently stolen around a dozen bags a year, and takes walks at a rate a tick or two above league average (8.2% across his career) — plus the aforementioned improvements on defense.

But, I ask you, what if he made a little more contact? Contact is good for hitters! It’s generally something you strive for. Allow me to present you with an incredibly simple graph:

That is what we in the industry (which one? Not sure) like to call "trending in the right direction." A career-best 12.1 K% plus a stellar 12.1 BB% have helped Semien hit the ground running in 2019, posting a line of .316/.396/.506 over 91 plate appearances. Am I suggesting that Semien is going to hit .320 for the rest of the year? I am not. Am I suggesting that an early display of improved plate discipline from him could foreshadow a step forward for him this year? We’re getting warmer!

This feels like the part of the article where I yell out "sample size" before anyone beats me to it, so, you know, sample size and all that. But stick with me! Plate discipline stats tend to stabilize relatively quickly — K% between 100 and 150 plate appearances depending on who you ask, BB% a bit longer — and digging into the numbers suggests real adjustments at the plate that could help to prolong this early success.

He’s basically still swinging at the same rate that he has in the past, but Semien is particularly making better contact on pitches in the zone — thus far in the young season, he has posted a whopping 92.9 Z-Contact%, good for 17th in baseball and far above his already-solid career average of 86.7%. (It’s also worth noting that this is the second straight season that he has improved upon his Z-Contact% from the year prior — 88.3% in 2018 — and this combined with his newfound defensive prowess indicate an impressive ability to adapt and learn at the major league level.)

Let’s compare last year’s zone profile versus this year to see where he might have made some adjustments. The left shows Semien’s whiff rate from 2018, while the right shows 2019.

Already it’s clear that he’s seeing pitches up in the zone better than he has last year, and indeed across his whole career, a place that has been a relative weak spot for him. He’s creating fewer holes for pitchers to attack him in the zone, which is a clear positive, especially for a hitter with a discernible eye at the plate. It’s worth noting that not all pitches are created equal, and just because he’s making contact doesn’t mean it’s always good contact. (Hold onto that point.)

He is, however, also making a lot of really good contact. He’s posting an exit velocity of 88.6 MPH this year, up from 86.6 MPH in 2018 and even besting the 87.8 he average in his 27 home run season. So we have Semien a) improving off an already good walk rate; b) making more contact that he ever has before; and c) hitting the ball harder than he ever has before.

All of these indicate why his hot start may not be just smoke and mirrors. Yes, the high batting average is buoyed by a .333 BABIP and both are due to come down eventually, but Baseball Savant gives him an expected batting average of .279 based on his quality of contact so far, and with his great on-base skills complementing the hit tool, it stands to reason that the shortstop could be in for his best offensive season yet…

...but there’s a catch. (There always is!)

Here’s the thing about Marcus Semien in 2019: the dude can’t stop hitting ground balls. Like, he’s just flat out hitting way more than you want if you’re trying to tap into that lost power stroke. Take a look at another simple graph that shows something much more complex.

I think I audibly gasped when I saw this. His launch angle, correspondingly, is down to 11.3, a precipitous drop off from his average of 14.9. It shouldn’t come of too much of a surprise given what we’ve talked about thus far — by cutting some loft out of his swing, it stands to reason that he would make more contact. And ground balls can certainly work, especially if you’re hitting them hard like Semien is, but they’re of less use if you want to be more than a shortstop with light pop, a breed of player that is becoming increasingly rare these days. One more graph (okay, two side-by-side) and then I’ll stop bombarding you.

While he’s laying off pitches on the inside of the plate more, he’s gotten more aggressive with pitches low and away, which is where historically he’s seen a majority of his ground balls come from. Perhaps it’s him trying to generate more plate coverage with his swing, and it’s promising that he’s taking the ball the other way more than normal this year, rather than trying to turn on those pitches way. But his batted ball profile thus far has indicated looked more like 2018’s Brian Anderson or Ketel Marte — in other words, a contact hitter who can sock a dozen dingers and consistently get on base, but not anyone who will blow the competition out of the water.

Semien has already hit three home runs this year, and his ISO of .190 is hovering around its 2016 levels, so whatever he’s doing so far seems to be working (the potential for a juiced ball probably hasn’t hurt either). But if that 13.6 FB/HR% does eventually take a hit and come back down to his career average around 10%, it’s possible he’ll need to readjust — again.

All this to say that Semien really does seem to have made discernible improvements this year. The improved contact rate is an astounding adjustment, and taking that along with a his improved exit velocity indicate that he’s tinkering under the hood to some success. The ground ball rate is startling, but not alarming in any sense. He has tools in the rest of his profile to show that he’ll likely continue to be a reliable option for the A’s at shortstop.

He’s already among the better shortstops in the American League. But if he’s able to find a happy medium between that contact rate and the loft in his swing, he’ll shed that consistency for the better, with the opportunity to punch his first ticket to the All-Star game — and maybe more.

All stats courtesy of FanGraphs, and zone profile heat maps courtesy of Brooks Baseball.