Defining Marcus Semien’s Role on the 2015 Athletics

Bay area native and Cal-alum Marcus Semien was acquired by the Athletics from the Chicago White Sox in the Jeff Samardzija trade this offseason. Semien has shown some potential of being a solid infielder at the minor league level, but has yet to put it all together over a full productive year in the big leagues, hitting .234/.300/.372 in 255 plate appearances.

He’s only 24, so he still has room to grow, but his role on the 2015 team is unclear for now. He could play well enough to earn the everyday shortstop job, he might be the right-handed half of a platoon with Eric Sogard, or he might just be a backup who fills in for injured/ineffective players all over the field.

But simply looking at his overall numbers in the big leagues is not enough to try to predict his success in 2015. After initially struggling in an everyday role with the big league club in April, he started playing sporadically in May, which did not help him. At the end of May, his slash line was .222/.292/.333, and he was sent down to AAA.

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In AAA, he seemed to make the necessary adjustments, hitting .267/.380/.502 with 15 home runs in 366 plate appearances. He also improved his plate discipline, walking 53 times and only striking out 59 times.

He was rewarded for his improvement with a call-up to the big leagues in September, when rosters expanded. He slashed .273/.333/.485 while playing regularly at either second or third base.

The A’s are hoping that the Semien in April and May is gone, and that the production he showed in the minors and in September with the White Sox is legitimate. Fangraphs steamer projections certainly think so, projecting him for 2.2 WAR next year.

Semien’s main competition for playing time will probably be Eric Sogard, Sam Fuld with honorable mentions Tyler Ladendorf and Andy Parrino if they have success in Nashville. If Fuld and Sogard outperform Semien in spring training, they will probably both be regulars in the lineup, and Semien could be shifted into a platoon with Sogard at shortstop.

Semien’s lefty/righty splits at both the minor league and major league level support platooning him. He had a .293 batting average against lefties, .235 against righties in the minors, and a .271 average against lefties, .212 against righties in the majors.

Personally I’m happy with the platoon system when the splits warrant it, but even though Semien’s do, his platoon partner would probably be Eric Sogard, who hit .228 against righties last year, or Sam Fuld, who actually has reverse platoon splits (.229 against righties).

If there’s no significant offensive advantage from platooning, it makes more sense to just let the better player get every day playing time. That’s especially true in this case, when all three players are strong defenders, so their only distinguishing factor is their offense.

In this case, the difference between Semien’s offense against righties and Sogard’s or Fuld’s would be minimal, so playing Semien at shortstop every day would be the best idea. He’ll probably have a short leash, thanks to the A’s depth, but right now that seems like the best role for him.