Before the season, If I’d asked you which player would lead the A’s in WAR, the answer would have undoubtedly been Matt Chapman. He led the way by far last year, exceeding 8 bWAR and 6 fWAR, and indeed he’s mostly repeating that performance. He’s posting another strong season at the plate and league-leading defensive metrics in the field, placing him in the top dozen in MLB on each WAR scale.
But Chapman does not have the highest mark on the A’s this year. That honor currently belongs to Marcus Semien. And again, it’s not because Chapman got worse — Semien has simply been incredible.
Semien’s breakout season is no secret, and in fact we ran an article about it in late-June, with an emphasis on his ever-improving plate discipline. By the All-Star break he had a 114 wRC+, his first time in triple-digits after a previous career-high of 98, which would already constitute a huge jump. But what you might not realize is just how much better he’s been since then.
Semien, 1st half (424 PAs): .271/.349/.448, 14 HR, 114 wRC+
Semien, 2nd half (269 PAs): .298/.387/.617, 16 HR, 163 wRC+
His OPS since the All-Star break is 1.004, and his 163 wRC+ ranks him 12th among all qualified MLB hitters in the second half of this season. His overall 133 wRC+ for the year ranks him in the Top 30 in the majors, and among the everyday A’s it puts him behind only Mark Canha and Matt Olson. He’s no longer just a guy who worked his way into being a plus defensive shortstop. He’s now an outright star on both sides of the ball, and he’s going to finish Top-5 for the MVP award, maybe even Top-3.
The latest improvement is mostly due to an uptick in power. Since the All-Star break he’s nearly doubled his rate of homers per plate appearance, and also increased his rate of doubles and triples, helping him tack on nearly 200 points to his slugging percentage in his second-half split (and about 150 points to his isolated slugging). He’s also done all this without sacrificing any of the elite plate discipline that he showed in the first half, as both his walk rate (10.8% up to 11.9%) and his strikeout rate (13.2% Ks up to 15.6% Ks) bumped up a point or two but generally stayed in line.
In other words, this isn’t just some BABIP mirage. Semien is legitimately destroying the ball these last couple months. His Statcast xwOBA was a decent .325 in the first half, but since the break it’s an enormous .382, which trails only Olson (by four points) among A’s regulars and ranks among the top couple dozen in the majors — and meanwhile the league as a whole has dropped five points in the second half (from .321 down to .316).
Granted, some of that power surge will presumably be due to the juiced ball, but the rest of the majors has enjoyed the same benefit and hasn’t exploded to the extent that Semien has. His 16 dingers are tied for 21st in MLB in the second half, whereas he was tied for 78th at the midseason break. You can put whatever 2019-related asterisks you want on this performance, and it won’t change the fact that Semien is on absolute fire. His rate of barreling the ball has nearly doubled from the last couple years.
If you want an explanation, look toward that expert plate discipline. He’s laying off a lot of the offspeed and breaking stuff that he used to chase, and doing a better job of either waiting for his pitch or taking the walk if he never gets that pitch. His rates of walks, Ks, and swinging strikes are all career-bests by comical margins — and we already knew that his bat had some thump hidden within, just waiting to be unlocked, based on his 27 dingers from 2016. And for good measure, he’s also doing slightly more damage than he used to against that secondary stuff, while also just annihilating fastballs like never before.
Put it all together, along with positive defensive metrics at the most valuable position other than catcher, and Semien has accrued 7.0 bWAR and 6.6 fWAR. Chapman is within a win of both marks for the team lead, thanks in part to having superior defensive value even after factoring in Semien’s larger positional adjustment as a shortstop. But Semien is on top, ahead of Prime Chapman, due largely to an offensive breakout that has him among the very best hitters in the majors since the All-Star break. And even if he never repeats the full extent of this year’s 30-homer onslaught, there’s good reason to be believe that his overall improvement as a hitter is absolutely real.