There are four big-name free agent shortstops available in the market this winter -- Xander Bogaerts, Carlos Correa, Dansby Swanson, and Trea Turner -- and in some ways, it’s quite easy to tell them apart. Which one is the youngest? Correa, though they’re all within two years of one another. Which one is the best hitter? In 2022, it was Correa; during all their careers, it’s also been Correa. Which is the fastest? Turner, obviously.

Now: Which one is the best defender? The answer is: It’s complicated.

It is, of course, a vital question for a shortstop you’re going to have to commit five-plus years to, and it’s an issue that’s more than a little messy, simply because three of them are coming off fielding seasons that -- by the leading metrics, anyway -- weren’t exactly in line with what they’d done in the past.

Take the names out of it, and here’s what the four top shortstops just did.

• Poor reputation/metrics before a solid 2022.
• Excellent reputation/metrics before a modest 2022.
• Decent reputation/metrics before a fantastic 2022.
• Inconsistent reputation/metrics before an average 2022.

Can you tell who is who? They’re listed in the same order as above -- Bogaerts, Correa, Swanson, and Turner -- and what do you make of any of that? Maybe, perhaps, it’s the nature of single-year defensive metrics, which are notoriously less accessible than single-year hitting stats. But maybe it’s evidence of real changes, either positive or negative, and teams are going to want to figure that difference out, particularly with 2023’s rules limiting shifting.

Let’s help them. What kind of fielders are any of these guys?

Bogaerts (turned 30 in Oct.)

• Outs Above Average (+5 // 88th percentile)
• Sprint Speed (27.9 ft/sec // 64th percentile)
• Arm Strength (82.1 MPH // 31st percentile)
• Free agent profile

Bogaerts spent some time as a third baseman early in his career before becoming Boston’s full-time shortstop, and for years it was thought that’s where he’d end up -- playing a position that wasn’t shortstop. That’s because by Defensive Runs Saved, which predates Statcast, he was the weakest shortstop in baseball from 2014-’21, at -55 DRS. By Statcast’s Outs Above Average, over 2016-’21, he was second weakest, at -41 OAA.

Say what you will about defensive metrics -- when two independent systems agree like this, you know there’s something going on there. Another year like that, and Bogaerts might not even have been considered a shortstop headed into free agency. Except, in 2022, something weird happened: He was good. OAA had him as +5, up from last year’s -11; DRS had him as +4, the first year on record he wasn’t a negative. He was, improbably, named a Gold Glove finalist.

So what happened here? To hear Bogaerts tell it, it came down to his own hard work and preparation.

“We started doing some different drills before games that has helped me a lot,” he told NESN, praising his coaches about work that began in 2021, and worked on his pre-pitch focus as well. “I wouldn’t say I was lazy with my pre-pitch,” he told the Athletic, “but I would say maybe I didn’t think it affected me as much as if you do it with intent, and correct.”

There’s more. He worked on drills aimed at improving his hip mobility, and, also according to the Athletic, “one of the biggest changes Bogaerts made was in narrowing his base in his pre-pitch routine, which allowed him to come in on balls quicker.”

To pick a few plays at Fenway Park (all with righty batters and no runners on) over the last two seasons, you can indeed see that he did just that. These are all frozen at the time of pitch release -- look at his feet. Base, narrowed.

Regardless of which change helped the most, Bogaerts did do a better job of just getting to the ball. OAA can be split into “getting to the spot” and “completing the play,” and in the former, just getting to the ball, Bogaerts rated between average and terrible each year prior to 2022 -- when, for the first time, he was above-average, at +4.

But there’s something else, too. Bogaerts was very good on the right side of the diamond, posting a +5 OAA while shifted over. Meanwhile, he was just OK at the traditional shortstop spot, with a -1 mark. That’s basically average, so it’s hardly unplayable. It’s just something to keep in mind when next year’s rules prevent shortstops from playing on the right side.

Going back to 2016, it’s even starker. 

• At shortstop area: -41 OAA
• At second base area: +7 OAA

His arm is of below-average strength for a shortstop, so maybe second base makes more sense than third for a future move anyway. 

Our take: He’s probably fine at short for another year or two, but he’ll be playing another spot by the end of this contract.

Correa (turned 28 in Sept.)

• Outs Above Average (-3 // 18th percentile)
• Sprint Speed (27.1 ft/sec // 45th percentile)
• Arm Strength (88.0 MPH // 72nd percentile)
• Free agent profile

Bogaerts was a poor fielder who unexpectedly got graded as a good one, though with considerable circumstantial evidence to support why. What, then, to make of Correa, who had rated as the third-best defensive shortstop over 2018-’21 (+49 OAA) before posting a surprising -3 OAA in 2022? (DRS did not have him as a negative, but, in dropping him from +20 to +3, saw him taking an even bigger step back than Statcast did.)

He still has one of baseball’s strongest shortstop throwing arms; that hasn’t changed. His speed has declined considerably, from 84th percentile as a rookie to just 45th in 2022. (He hasn't stolen a base since April, 2019.) That’s not ideal, though we’d caution against worrying about that too much, because shortstop defense isn’t about top-end running speed, and it was a similar 48th percentile in 2021, when he rated well.

On the other hand, again splitting OAA into “getting to the spot” and “completing the play,” and using the first as a proxy for range, the trend isn’t exactly going in the right way.

2018: +6 OAA
2019: +2
2020: +1
2021: -1
2022: -5

If this doesn’t feel like it matches the eye test, we agree. (Though there were some notable non-error plays, like this, and this, and this.) But defense, and defensive metrics, aren’t just about errors, they’re about plays not made -- whether they’re scored hits or errors -- and that does seem like what’s happening here. Compare how he got to this year’s -3 OAA vs. last year’s +11 mark.

In both years, Correa was demerited 27 OAA on hits that got past him. (Every fielder, by definition, is a negative on hits. That’s why they’re hits.) But last year, he sucked up so many batted balls that he earned +46 on outs, which far outweighed the -27 on hits. This year? Just an equal +27 on outs, which merely canceled out the -27 on hits. (Errors, in both years, made up the rest of the seasonal total.) The short version, then, even accounting for some missed time in 2022, is simply: Not enough chances turned into outs.

The famously analytically-inclined Correa is surely aware of this (as well as excited for the positioning ban). The speed probably isn’t coming back, but there were enough fluky bad plays within here that don’t seem skill-based that we’d be confident in his near-term defensive future.

Our take: Mildly concerned by the range/speed decline, but the strong arm, great track record, and relative youth should make him a no-brainer shortstop for the next several years.

Swanson (turns 29 in Feb.)

• Outs Above Average (+21 // 100th percentile)
• Sprint Speed (28.4 ft/sec // 79th percentile)
• Arm Strength (79.2 MPH // 15th percentile)
• Free agent profile

Swanson had a career year at the plate, taking a career 90 OPS+ into the year, then posting a strong 115 OPS+ while making his first All-Star team. It was similar on defense, too; while he’d been solid enough from 2016-’21 at +14 OAA, he had a massive fielding year, leading all shortstops with +21 OAA, earning his first Gold Glove in the process. If that sounds wildly out of step with his past, it was; then again, so was his hard-hit rate. Talk about a well-timed career year, all around.

Some of this is just going to come down to availability; if you’re on the field more than anyone, then all those extra nondescript grounders are going to add up to real value. Swanson was on the field more than anyone, as his 1,433 innings weren’t just the third-most by any shortstop in the previous 10 seasons -- they were the most in a season in Braves history (records on this go back to 1956, but it’s unlikely anyone topped him in a 154-game season).

To the extent that health is a skill, Swanson hasn’t been on the Injured List since 2019, and he’s missed only four games in the last three seasons -- which doesn’t include the 32 postseason games he’s started in that time as well. So that’s part of it: just being on the field and making the plays you’re supposed to make, despite one of baseball’s weaker shortstop throwing arms.

There are some notes to point out -- almost all of his gains came against righty batters, not lefties, and the Braves basically stopped shifting righties after ramping that up in 2021; he excelled going to his right (+12) after being poor in 2021 (-2) -- but there’s no smoking gun here, which is basically what Atlanta coach Ron Washington told The Athletic this summer, saying “There’s no play on that field he doesn’t make … He just don’t do it with any fanfare. But he knows how to do it.”

Last year, he missed 49 plays that had an out probability of more than 50%. This year, it was just 30, or only a handful per month. Sometimes, just making all those plays, day after day after day, adds up.

Our take: He probably won’t be this good again, but he’s been solid for several years now and there’s no reason to see that changing soon.

Turner (turned 29 in June)

• Outs Above Average (+0 // 47th percentile)
• Sprint Speed (30.3 ft/sec // 99th percentile)
• Arm Strength (83.7 MPH // 39th percentile)
• Free agent profile

Turner’s elite skill is obvious, and that’s his speed, where he’s rated in the 99th percentile or better in running speed in every single one of the eight years Statcast has been tracking. At some point, as he gets into his thirties, he’ll slow down, but there have been no signs of that happening just yet.

That’s not the same for the defensive metrics, though. After a peak in 2018-’19 (+17 OAA as a shortstop, and +10 DRS), it’s been somewhat downhill since then; over the last three seasons, he’s been -2 as a shortstop, and +1 as a second baseman, which is basically “he’s been an average fielder,” despite some high-profile October miscues.

Full stop there, for a second: “an average defensive shortstop” may not sound like much, but when it comes attached to a 20/20 player with a career 122 OPS+, who just scored over 100 runs for the third time, it’s an incredibly valuable player, even if it’s not likely to end with Gold Gloves. That's how, even with middling defensive metrics, Turner just posted 6.3 WAR (at FanGraphs), a year after an excellent 6.8 mark.

This could all end right there, that Turner gets to the plays (76% career success rate) he’s expected to (75% estimated success rate on the chances he’s seen). Which is fine. There’s one wrinkle, though.

“All I had to do was play three feet closer and the algorithm liked me more,” he told Ken Rosenthal in July, arguing that his poor early-2022 metrics were about positioning, and how he’s then graded on his opportunities. To his point, he was -7 OAA in April/May, then +7 OAA for the remaining four months -- and further, he did indeed play three feet closer as the season progressed. Maybe he just beat the system.

But it’s a bit of a chicken-or-the-egg situation here, because: Was he graded better because being shallower made his chances look harder? Or because he just played better? So far as Statcast is concerned, there’s a simple answer to that.

April-May: An average fielder would be estimated to convert 74% of Turner’s chances into outs. He converted 73%.

June-Sept: An average fielder would be estimated to convert 74% of Turner’s chances into outs. He converted 75%.

While defensive metrics aren’t infallible, it’s difficult to argue with “he just made more plays,” and the chances were considered identically difficult. It might just be Turner’s more effective playing in. 

Our take: An average shortstop with average metrics, so the numbers match the reputation, though a move to second base by 2025 doesn’t seem unreasonable. Maybe keep playing shallow, though.