Marcus Semien 2018: A Career Year?

by Phoenix Desertsong

Baseball fans love talking about career years for their favorite players. The 2018 A’s had a lot of good years from a lot of their players. But one of those players, Marcus Semien, had a lot better season that his baseball card stats would suggest. In fact, what drove Semien’s career year success was not his offensive stats, but rather his defensive stats.

According to FanGraphs, Marcus Semien compiled 3.7 WAR (Wins Above Replacement) in 2018. This beat his 27 home run “breakout” season in 2016, in which he earned 2.1 WAR. So, what took Semien from an average major league shortstop to an above average one? The key to his value lay in drastically improved defense at shortstop.

Marcus Semien has always hit for power. But he’s always suffered from low batting averages (career .249 BA), low on-base percentages (career .319 OBP), and erratic defense. He actually wasn’t bad on defense in 2015, but he was “worth” -15 defensive runs between 2016 and 2017. So, what changed?

Marcus Semien and His Improved Defense and Defensive Stats

A lot of people are skeptical of defensive statistics, as they tend to fluctuate significantly from season to season. However, consistently excellent defenders and consistently bad defenders usually are bore out over the course of a player’s career. Erratic defenders are harder to pinpoint. As we’ve learned over the years, defense is actually a quantifiable asset. It comes down to what plays a player “should” make.

In his career through 2018, these were Semien’s defensive stats broken down by the likelihood of a play being successfully made:

Impossible (0%) 0%
Remote (1-10%) 0%
Unlikely (10-40%) 11.3%
Even (40-60%) 15.7%
Likely (60-90%) 61.1%
Routine (90-100%) 95.9%

In 2018, these are his numbers

Impossible (0%) 0%
Remote (1-10%) 0%
Unlikely (10-40%) 12.5%
Even (40-60%) 21.1%
Likely (60-90%) 61.9%
Routine (90-100%) 96.8%

While those percentages are definitely better than his career averages - which are boosted by his 2018 numbers - they don’t seem like that much. Still, all you need are a handful of made plays in those 10-40% and 40-60% ranges to make a big difference in your defensive value.

Those numbers made Semien worth 9 Defensive Runs Saved and 6.4 UZR/150 (Ultimate Zone Rating per 150 games played). That’s well above-average, although not quite Gold Glove calibre. But what stands out about Semien’s year is how my OOZ (Out of Zone) plays he made: 133. Previously he had made 106 in 2016. His RZR (Revised Zone Rating) was .869, far above his career average of .803, which includes 2018.

This is definitely an improved defensive player. Will he keep this up? It’s completely possible, as defense is a skill that can be learned and improved over time.

Marcus Semien Batting in 2018

For a career year, you’d expect Semien to have a breakout with the bat. That’s not what happened at all. Marcus Semien had a batting average of .255, right in line with his career stats. His on-base percentage was merely .319 and his slugging percentage a fairly low .388. That’s not a great batting line. However, as he plays in Oakland, notoriously not a good pitcher’s park, that batting line of .255/.319/.388 is nearly league-average. He also was a positive on the basepaths with 14 stolen bases, although he was caught 6 times.

There are a couple of interesting things to point out, however. Semien saw more pitches at the plate in 2018 than ever before in his career: 2881. He also saw far more balls, 1102, than ever before. He also hit more line drives and fly balls than ever before, and had a career high 19 infield hits.

Is Marcus Semien Poised for a Better 2019?

When you see improvements across the board like this, it’s very likely you have an improving player. Marcus Semien is only 28 years old and in his prime. The Oakland A’s may enjoy even better results from their shortstop moving forward. If he’s able to produce even half of the defensive value that he did in 2018, he could be an above-average shortstop going forward.

While StatCast seems to think that Semien was a bit lucky with only a .299 expected on-base average (xwOBA) and .329 expected on-base average on contact (xwOBACON), he also had more batted balls in 2018 than ever. If Semien squares up just a few more fastballs going forward, this is a sneaky good, very underrated player.

While Marcus Semien may not be your first choice at shortstop for a fantasy baseball team, or even your fourth or fifth, he’s possibly not seen his best year yet.