As we saw last offseason, life on the free-agent market for 30-and-older free agents can be rough. Teams have been prioritizing youth over experience, for reasons of flexibility, health, projected performance and budget.
It makes for an interesting setup for this winter's class, because while we know that young stars like Bryce Harper and Manny Machado are going to strike it big, we don't know how some of the more veteran players will do. What we do know is that teams will be using any and all of the tools available to them to try to project performance over the next few years. After all, they won't care that, say, Ian Kinsler was a four-time All-Star between 2008 and '14. They'll care about what he can do in '19 and beyond.
One way to do that is by looking at a few of this year's over-30 free agents through the window of speed, specifically Sprint Speed, the Statcast™ metric that tracks top running speed in feet per second in a player's fastest one-second window. (Read more about how Sprint Speed works.)
Last year, we showed that (unsurprisingly) as a group, younger players tend to run faster. Early in the 2018 season, we looked at Matt Kemp's resurgence after claims of a winter of conditioning and found that it seemed legit, since he'd added a great deal of speed; last week, we used it to evaluate Josh Donaldson's free agency after several years of calf injuries.
Speed doesn't guarantee health, production or value. But it can help tell some new stories about names you've long known, especially when the players tell similar stories in their own words. Let's look at four of this offseason's prominent free agents (all traded during 2018) to see how their speed has changed -- not necessarily all in the same direction.
Looking up: Mike Moustakas
Last March, Moustakas settled for a surprising one-year deal to return to Kansas City, where he spent half the season before being traded to Milwaukee. He did more or less what he always does, which is to put up a slightly above-average low-OBP season with power (.251/.315/.459, 108 OPS+), though his slugging percentage dropped to the lowest level it had been since 2014.

Part of his free agency struggle was due to the qualifying offer he'd received; part of it was that few contending teams actually needed a league-average third baseman. He ended up being the 17th-most valuable third baseman among those with 400 plate appearances.
But part of it, according to a report in The Athletic (subscription required) last April, may have been about concerns over his health. 
"Moustakas knows the perception that he was not in top condition might have been a contributing factor in the limited interest he received as a free agent," wrote Ken Rosenthal. "But Moustakas, 29, addressed that criticism by getting in better shape, and GM Dayton Moore spoke excitedly last week about the slugger's off-season work, saying he is running as well as he ever has."
Moustakas has never been speedy, but his Sprint Speed had fallen dramatically. In 2015, it was 25.8 ft./sec., in the 29th percentile, below the Major League average of 27 ft./sec. By '17, it had fallen to just 24 ft./sec., the 9th percentile -- below-average even for catchers. That wasn't terribly surprising, because he sustained a serious right knee injury in '16 that required season-ending surgery, and then he dealt with soreness in the knee for much of the next season.
Moustakas Sprint Speed rankings
2015: 29th percentile
2016: 15th percentile (27 games)
2017: 9th percentile
2018: 26th percentile 
Moustakas found his lost speed in 2018. His 2017-18 jump, from 24 ft./sec. to 25.7 ft./sec., got him back to where he was in '15. It was also the largest increase of any qualified player in the game.

It's easy to see on a monthly basis, too, comparing his peak and average (on competitive runs) speeds. In 2018, his peak speeds were back in the 27 to 28 ft./sec. range they'd been pre-injury, but nearly as important, his average speed mirrored that closely. In '17, he'd been capable of short bursts, but the lingering soreness apparently prevented him from maintaining that as well. That didn't seem to be an issue in '18.

While it didn't improve his hitting stats -- see that slugging drop -- it might have helped with his defense, because he had a minus-8 DRS in 2017 before posting a +2 in '18. He even stole four bases, as many as he'd had in the last four seasons combined.
Ultimately, Moustakas still has to deal with being a good-not-great third baseman at a time when the position is stacked with talent, and in a market where teams may prefer to bet on Donaldson. But if this was a reason teams shied away last year, he can at least point to this improvement.
The effects of playing through injury: James Dozier
"It's been a struggle," Dozier said to the Los Angeles Times in September. "I've had a knee issue since the beginning of the year."
You don't need advanced data to know that Dozier's 2018 wasn't exactly what he was hoping for. This was a player who had put up five straight average or better seasons and received down-ballot Most Valuable Player Award support in '15, '16 and '17. But in '18, he hit just .215/.305/.391 with an 88 OPS+, which was about the same as Tim Anderson or Freddy Galvis, and it got worse after a trade to the Dodgers. With L.A., Dozier hit only .182/.300/.350. His once-strong defense suffered as well, falling to a career-low minus-8 DRS.
Interestingly, from a speed perspective, it looks like this began in 2017, when he had a strong season -- though amid reports he was playing through pain or a sore back.
Dozier Sprint Speed rankings
2015: 73rd percentile
2016: 71st percentile 
2017: 54th percentile
2018: 47th percentile 
You can see it in his monthly charts, as his peak Sprint Speed was generally just south of 29 ft./sec., where it had routinely been north of 30 ft./sec. in 2016.

Despite a crowded second-base market -- DJ LeMahieu, Jed Lowrie and Daniel Murphy are among the other options -- one poor year shouldn't be enough to eliminate Dozier as a possibility. He'd been too good for too long. He'll just have to prove the knee is healthy, however, if that really was the cause of his struggles. 
Holding steady: Andrew McCutchen
McCutchen turned 32 last month, and he's no longer the regular MVP Award candidate he was during his peak years in Pittsburgh. He's no longer even a center fielder, becoming a full-time corner outfielder for the first time in 2018 with the Giants and Yankees. 
This is about the age where you would expect a player with more than 1,500 career games to start to slow down, and maybe that's what will happen. But the remarkably durable McCutchen -- who has taken at least 640 plate appearances in every full season of his career dating back to 2010 -- hasn't really shown any indication that this is happening to him, at least not yet. Among regular right fielders, only two (Travis Jankowski and Avisail Garcia) were faster. 

McCutchen Sprint Speed rankings
2015: 87th percentile
2016: 95th percentile 
2017: 90th percentile
2018: 88th percentile 
The monthly data tells a similar story, though it's interesting to see at least a slight divergence between his peak and average. It does show, however, that the top speed is still there when he needs it; when he grounded out against the Tigers on Sept. 1, his 30.6 ft./sec. speed was his second-fastest of the last four years. (Interestingly, it was his Yankees debut.) 

We don't have this kind of data from back in 2010, when McCutchen was 23 and stealing 33 bases, while still playing center field. If he's not quite what he was then, that would make sense. But in '18, McCutchen hit a solid .255/.368/.424 and had a 118 OPS+ when accounting for the effects of what AT&T Park does. It's not the 134 OPS+ he's put up over his full career, but it is basically the 115 OPS+ he's had over the last three years.
That's a solidly above-average player, one who's a perfect fit for a contender with a short-term corner-outfield need -- perhaps Cleveland, Colorado or Atlanta. 
Recovering: Daniel Murphy
It's easy to forget that Murphy stole 23 bases in 2013 for the Mets, but speed was never really his game. Instead, the story of his rebirth as a high-contact power hitter is near-legendary at this point, and his .326/.375/.542 line in 2016-17 made him one of the 20 best hitters in baseball.
At first glance, 2018's .299/.336/.454 doesn't quite match up. Of course, Murphy underwent microfracture knee surgery in the offseason, and he didn't make his season debut until June 12. When he did, he wasn't effective. His .200/.231/.240 line was the worst month of his career. 
But it got a lot better after that. From July 1 on, both with the Nationals and the Cubs, Murphy hit .317/.355/.493 across 299 plate appearances. If it's not quite his 2016-17 peak, it's not far off, and it made him one of the 40 best hitters with at least 250 plate appearances in that span, up there with bats like Rhys Hoskins and Edwin Encarnacion.
Unsurprisingly, the data shows that either Murphy's knee wasn't fully healthy or that he was (understandably) taking it easy as he worked his way back into the lineup. In June, his peak and average scores were easily his lowest of the four seasons of Statcast™. They steadily increased each month after that.

In fact, Murphy's two fastest Sprint Speeds of the season both came in late September, when he beat out two infield hits to shortstop in three days (though neither drew a throw, to be fair). 
Murphy Sprint Speed rankings
2015: 28th percentile
2016: 43rd percentile 
2017: 36th percentile
2018: 23rd percentile 
It's an open question as to whether a team will still consider Murphy a second baseman or more of a first baseman/designated hitter. But based on his performance after his slow start last year, the bat still looks sound. If that's because of his knee, well, no one expects another 23-steal season. The foot-speed data sure looked promising as 2018 went on, however.