Marcus Semien got into 768 regular-season games on defense for the A's after they traded for him in the winter of 2014-15, and he played shortstop for every single one of those appearances. He played so much shortstop that only one player, Boston's Xander Bogaerts, got into more games at the position from 2015 through 2020. Semien played shortstop, and he played only shortstop.

But in 2021, after joining the Blue Jays on a one-year, $18 million deal, Semien is expected to move over to second base, since Toronto is committed to Bo Bichette on the left side. Although Semien has some experience at the keystone -- 29 games for the White Sox at the start of his career -- the last time he was actually in a Major League game as a second baseman came way back on Sept. 26, 2014, when his right-side partner was Paul Konerko and his manager was Robin Ventura.

It's been a minute, anyway, and with defensive improvement a well-stated goal for Toronto heading into the new season, how Semien can adapt to his new position is going to be one of the more interesting storylines of camp. Except ... is it a new position? What is a position, anyway?

It's true that it's been nearly seven years since Semien last had a "4" next to his name in the box score. It's additionally true that 350 players have gotten into at least one game as a second baseman since Semien became a full-time shortstop in 2015, including such unexpected names as Anthony Rizzo and Mookie Betts. But it hasn't really been that long since he played on the right side of the infield, because he was doing it as recently as ... last year's playoffs. Even for an A's team that didn't shift all that much compared with the rest of the Majors, Semien still found himself on the other side of the bag enough to gain plenty of familiarity there.

So is this a second baseman? Or a shortstop playing out of position? Does it even matter?

What about this?

Or this?

Sure looks like a second baseman to us.

Dating back to 2017, we found 213 batted balls where Semien had started in the second baseman's traditional area and had the opportunity to make the play. (Remember -- he was always listed as a shortstop, every single time.) Based on the difficulty of each play, based on the distance, time, runner foot speed and other factors, an average fielder would have been estimated to convert 91 percent of those plays into outs. Semien turned ... 92 percent of them into outs. He was fine.

Now, that's looking only at batted balls hit to him, and that's the "easy" part, all things considered. What's generally considered more difficult is turning the double play, since you're coming at it from a different angle than you're used to, especially with the runner bearing down on you.

In some sense, that's just not the concern it used to be; with strikeouts, home runs and fly balls all on the rise, double plays and double-play opportunities have never been lower. In 2020 there were just 0.8 double plays per game, the lowest since 1920. But that's not because teams are worse at turning it, because the opposite is true. If we look at the pitch tracking era of 2008-20, this past season saw 32.7 percent of possible ground-ball double-play situations -- that's zero or one outs, with a runner on first (at a minimum), and a ball hit on the ground -- turn into two outs. That's the highest rate on record. The chances come less often, but teams are better than ever at converting them.

It's also not something Semien is unfamiliar with. When the Blue Jays approached him, they asked him about his preference between second base or third, knowing that Cavan Biggio could handle either.

"I really love shortstop, but if I had to choose, I'd choose second base [over third base]," Semien told MLB Network earlier this month, "because in the shift with Oakland I played over there a lot, even worked on turning double plays a lot, so it's something I will be working on every day in Spring Training ... that double-play turn."

Either way, Semien looked OK doing it in 2013 for the White Sox as an actual second baseman:

He looked OK doing it in 2019 for the A's as a shifted-over shortstop.

Is it about starting a double play from the right side? In 2019, this one sure looked like a traditional 4-6-3, even though it went into the books as a 6-5-3 (that's Matt Chapman, third baseman, making the turn), because again, what even are positions, anyway?

Semien would, obviously, not be the first second baseman who arrived from another position, though not always from shortstop. Max Muncy doesn't fit the traditional profile, and he's managed fine in limited opportunities for the Dodgers. Third baseman Mike Moustakas played some second base with the Brewers in 2019, and signed with the Reds in 2020 with the intention of playing second base. When we looked into the idea last winter, we noted that, like Semien, Moustakas had seen some time on the right side as a shifted third baseman, notably making a nice play to rob Cody Bellinger of a hit in the 2018 playoffs.

At the great risk of taking too much away from a mere 32 games at second in 2020, Moustakas was ... fine. He received 68 tracked fieldable chances. He was expected to convert 90 percent of them based on their difficulty; he actually converted 91 percent. If not a plus there (DRS had him at minus-3, for comparison's sake), he was competent enough, and surely Semien's reputation is one of having more defensive skill to begin with.

Basically, if Moustakas can turn a 5-4-3 double play like this, with the runner bearing down upon him, there's little reason to think Semien couldn't.

What's somewhat uncertain is whether Semien is the full-time, no-questions-asked second baseman, or if he'll see time at shortstop when Bichette is unavailable, or if he'll be an option at third base if necessary. But if he's playing second base regularly, he'll join a shockingly limited club. He'd be just the second player this century -- and one of only a dozen in history -- to have a season in which 90 percent of his games come at second base, directly following three consecutive seasons in which 90 percent of his games came as a shortstop.

The only other one to do it in the 21st century? Dee Strange-Gordon, who spent most of his first three years at shortstop for the Dodgers, then moved to second base in 2014 and immediately made the All-Star Game. (It's noteworthy that after years away from the position, Strange-Gordon may get another chance at shortstop for the Reds in 2021.)

Interestingly, of the other 11, five of them -- Ricky Gutierrez, Rey Sanchez, Pat Meares, Mark Grudzielanek and Jay Bell -- came in a short span between 1996-99. Now, this doesn't count in-season shifts, like when Starlin Castro, who had spent the previous five full seasons at shortstop for the Cubs, moved over to second base in August 2015 after Chicago promoted Addison Russell from Triple-A to play short. Then again, that's not really what Semien is doing, either; he gets a full Spring Training to prepare. None of this gives us a lot of history to look back upon, other than the general notion that second base is lower on the defensive spectrum than shortstop. Yet as Semien noted, there's a lot of similarities.

"Second base and short, you can still work on the same things, besides the double-play turn," Semien told MLB Network.

We'll buy it. He's shown it. There's been considerable disagreement in regard to how much, or if at all, his fielding has improved since his early days, though the hidden secret in baseball is that second base isn't really a defense-first position any longer. (As though the presence of Muncy and Moustakas didn't give that away; when we wrote about Moustakas last year, we noted that between 2008 and '19, second basemen had a drop in opportunities of 25 percent, thanks to the changes in the way the game is played.)

The good news for the Blue Jays is that Semien's seemingly down-looking 2020 with the bat wasn't all that bad; aside from playing through injury, a hot postseason pushed his overall line north of league average. The better news is that if Bichette is injured again, they have a better option at short than Joe Panik or Santiago Espinal this time. The best news? Semien may not have been a second baseman in years, but he's played second base. It's not that new to him. He'll be just fine.