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Marcus Semien has become a legitimate leadoff hitter

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He’s finally displaying the on-base skills he showed as a prospect.

MLB: Seattle Mariners at Oakland Athletics Stan Szeto-USA TODAY Sports

The saying “you can’t predict baseball” has perhaps never been more true than it is today. It seems that records are broken every night and players continue to improve their game at a shocking rate.

In 2014, the Houston Astros designated outfielder J.D. Martinez for assignment. He reinvented his swing and is now one of the most feared power hitters in the game. Listed at just 165 pounds, Arizona Diamondbacks infielder Ketel Marte entered the 2019 season with just 22 career home runs. As of Monday morning, he ranked seventh in the National League with 20 bombs. In 2015, then-Miami Marlins outfielder Christian Yelich hit just seven home runs and posted a 62.5% ground ball rate, the highest among all qualified hitters. Today, his 29 homers lead all of baseball.

The list goes on. In today’s age of analytics, players have more information available at their fingertips than ever before. Today’s baseball might be remembered as the era of improvement.

And Oakland Athletics shortstop Marcus Semien might be the most improved player of them all.

That’s a bold statement. After all, Yelich is the reigning NL MVP, and Martinez just became the first player to win a Silver Slugger at two positions (designated hitter and outfield). The Los Angeles Dodgers infield features two outcasts-turned-superstars in Justin Turner and Max Muncy, and there are countless other fantastic stories of career revival across the game.

But Semien’s improvements might be the most drastic of them all. In just a few short years, he went from being the worst defensive shortstop in the game to possibly one of the best, while also transforming from a free-swinger to a complete hitter with elite plate discipline.

Semien’s early defensive struggles and eventual rebound are well-documented, so let’s talk about his hitting. As a minor leaguer, Semien’s calling card was his outstanding plate discipline. While he was also a power-speed threat, his OBP skills really made him stand out.

Marcus Semien, minor leagues

Year Level G PA BB% K% OBP wOBA wRC+
Year Level G PA BB% K% OBP wOBA wRC+
2011 Single-A 60 262 8.4% 20.2% .320 .318 92
2012 High-A 107 487 11.3% 19.9% .362 .373 131
2013 Double-A/Triple-A 137 625 15.7% 14.4% .401 .402 157
2014 Triple-A 83 366 14.5% 16.1% .380 .391 142

The A’s clearly trusted Semien’s consistent minor league numbers, as he spent significant time near the top of the order during his first season with the club. In 2015, Semien batted either first or second in 48 of the 155 games he played.

But he probably shouldn’t have. In that season, he posted his highest strikeout rate, lowest walk rate, and lowest OBP as a professional. His 97 wRC+ was acceptable, especially for a shortstop in his first full season, but it was supported by surprising power rather than his usual on-base ability.

In 2016, Semien doubled down on that power. He slugged a career-high 27 home runs, leading all full-time MLB shortstops. The power surge led to a slight uptick in walks and strikeouts, and his BABIP took a massive dive from .310 to .268, likely due to an increase in fly ball rate and launch angle. In total, despite gaudy power numbers, Semien was once again a slightly below average bat, posting a 98 wRC+.

It seemed like Semien might be turning a corner in 2017 and returning to his minor league ways. Through the first 11 games of the season he posted 10 walks in 46 plate appearances, a walk rate of 21.7%. But on April 16 he went down with a broken right wrist and ended up missing almost three months. Upon his return, the plate discipline improvements disappeared and he finished with a 96 wRC+.

Through his first three seasons with Oakland, Semien was a remarkably consistent (although somewhat disappointing) hitter. He combined middle-of-the-road power, speed, and discipline to provide slightly below average offensive value. Heck, even in 2018, he posted a 95 wRC+, right in line with his career norms. But something was different.

Marcus Semien, MLB, 2015-18

Year G PA BB% K% OBP wOBA wRC+
Year G PA BB% K% OBP wOBA wRC+
2015 155 601 7.0% 22.0% .310 .301 97
2016 159 621 8.2% 22.4% .300 .311 98
2017 85 386 9.8% 22.0% .325 .315 96
2018 159 703 8.7% 18.6% .318 .314 95

In 2018, Semien quietly maintained some of his walk rate gains from 2017. He also cut his strikeout rate significantly, while still hitting for a bit of power (15 HR, .133 ISO). These improvements were overshadowed by the surprising success of the team around him and perhaps by his own defensive improvements. So, again, Semien was just a slightly below average hitter, and one whom Oakland probably didn’t expect much more from in 2019.

But it looks like the breakout has finally come. As the A’s near the halfway point of the season, Semien has been one of the team’s best hitters, as his 117 wRC+ and .342 wOBA rank fourth behind superstar Matt Chapman, the surprising Mark Canha, and slugger Matt Olson.

Marcus Semien, MLB, 2019

Year G PA BB% K% OBP wOBA wRC+
Year G PA BB% K% OBP wOBA wRC+
2019 80 365 11.5% 13.4% .359 .342 117

Semien’s walk rate has spiked to a career high, as his strikeout rate has dropped to a career low. Meanwhile, his .161 ISO is the second highest mark of his career, while his .299 BABIP is right where it belongs. His 0.86 BB/K rate ranks eleventh among all qualified MLB hitters. It looks like Semien has finally turned into the OBP threat he was in the minor leagues, and the A’s have rewarded him by making him their leadoff man.

But maybe we should have seen this coming. The 28-year-old has been slowly improving almost across the board since his first season in Oakland. Via FanGraphs:

Marcus Semien career plate discipline, by season
FanGraphs.com

Semien has slowly increased his contact rate, while decreasing his swing rate and swinging strike rate and seeing fewer pitches in the zone overall. Specifically, he has made significant improvements on pitches in the zone, seeing an increase of nearly six percentage points in zone contact rate since 2016.

In 2019, Semien is seeing fewer fastballs than ever before, but his response has been incredible. According to Brooks Baseball, he has posted career-low whiff rates against all three pitch categories — 6.67% against hard pitches, 10.07% against breaking balls and just 6.90% against offspeed. He’s especially improved against offspeed pitches, which used to eat him up, as he’s doing a much better job of laying off the ones he can’t handle. In general he is controlling the strike zone incredibly well, with his only real struggles coming against pitches near the top of the zone.

Thanks to his improved plate discipline, solid power and speed, and fantastic defense, Semien has been one of the most valuable players in the game. His 3.5 bWAR ranks eighth among all MLB hitters, while his 3.0 fWAR ranks 11th. This is an incredible turnaround for a player who, in 2015, ranked just 109th out of 141 qualifiers with 1.4 fWAR.

There’s obviously room for some regression here. The numbers suggest Semien is one of the best defenders in baseball, and I’m not sure that’s quite true. It has also been just half a season — if Semien has a poor second half, his discipline numbers could fall back near his career norms. But at the very least, he clearly belongs at the top of the lineup right now, as a good overall hitter and one who can get on base.

But I think, to a very notable extent, Semien has improved on both sides of the ball. Every defensive metric agrees that he is a great defensive shortstop, and his discipline improvements were gradual and are supported by his lengthy minor league track record.

On Monday, A’s General Manager David Forst included Semien as one of many young players the team is looking to extend. With the shortstop set to hit free agency following the 2020 season, I hope the team makes an extension one of their top priorities. Before 2019, Semien was just a solid everyday regular. But now, he has turned himself into an indispensable asset, both at the top of the order and at the most demanding position on the field.