Will Leitch took an in-depth look at the game in 2019 with a series exploring Major League Baseball's Data Decade. From the best World Series, to the best starting pitchers and more, Leitch ranked, dissected and celebrated all the things we loved most about the Great American Pastime during the past 10 years.

Perhaps no position in baseball has changed more over this past decade than the relief pitcher. In 2010 -- as in most of the last 30 years of baseball -- you had your closer, and everything funneled toward him. In 2019, there are still closers, but the job is much more fluid, and fragile, and then sometimes you actually start the game and they call you the “opener.” The way reliever usage is changing so rapidly, one wonders what the heck this position will look like in 2029. Will we even use the word “relief” anymore?

So we look at the 10 best relief pitchers of this decade. It may be the last decade we can do so.

Here are the best this decade.

1. Craig Kimbrel (ATL 2010-14, SDP 2015, BOS 2016-18, CHC 2019)
It didn’t go well for the Cubs in 2019. But let’s not forget who this guy is. The Braves knew what Kimbrel was from the very beginning; he never started a single game in the Minor Leagues. He gave up only one earned run in 20 2/3 innings his rookie season in 2010 and was dominant every season after that, leading the NL in saves four times and making seven All-Star teams. Kimbrel had a career 41.6 percent strikeout rate, which is downright absurd.

2. Kenley Jansen (LAD 2010-19)
Straight from the Mariano Rivera school of throwing one pitch over and over until someone proves they can hit it -- psst, it’s a cutter -- Jansen has been remarkably consistent since he arrived in Los Angeles in 2010. (Which happens when you have perfected your one pitch.) His best season was 2017, when he led the NL with 41 saves, had a 1.32 ERA and finished fifth in NL Cy Young Award voting (and 15th in NL MVP Award voting, for that matter). Plus: Jansen invented the intentional balk, which is worthy of Cooperstown consideration on its own.

3. Aroldis Chapman (CIN 2010-15, CHC 2016, NYY 2016-19)
Off-field issues aside, Chapman so revolutionized baseball this decade that Statcast’s velocity leaderboard needed a special filter for Chapman, who threw so much harder than everyone else (until Jordan Hicks came along). The Reds were still fiddling with the possibility of making him a starter when they signed him, but after four All-Star appearances with the team, they mercifully dropped that. The Cubs brought Chapman in to help win a World Series, but then he went back to the Yankees (who originally acquired him from Cincy) to try to win another one. He no longer throws harder than anyone in baseball. But yet, in 2019, Chapman might be having the best year of his career.

4. Wade Davis (TBR 2010-12, KCR 2013-16, CHC 2017, COL 2018-19)
Davis was actually starting games up until 2013, so it’s cheating a little bit to put him on this list … but what a reliever he became, when he finally become one. (And he wasn’t that terrible of a starter either.) Once the Royals installed him in the bullpen in 2014, he went on a truly astounding three-year run, putting up ERAs of 1.00, 0.94 and 1.87 from 2014-16. And, of course, in the middle there … Davis finished off a World Series.

5. Zack Britton (BAL 2011-18, NYY 2018-19)
Britton was another converted starter, but unlike Davis, he was a pretty bad one for the Orioles. But once they put him in the 'pen, he became one of the most feared pitchers in baseball. Britton's sinker was basically unhittable for several years, and he was the linchpin of some O's teams that came this close to finally breaking through. One of the reasons they didn’t may have been manager Buck Showalter’s infamous decision not to use Britton in the 2016 AL Wild Card Game loss to Toronto.

6. Fernando Rodney (LAA 2010-11, TBR 2012-13, SEA 2014-15, CHC 2015, SDP 2016, MIA 2016, ARI 2017, MIN 2018, OAK 2018-19, WAS 2019)
As you can see in the previous parenthesis, Rodney has been … well-traveled this decade. Rodney’s longevity is his most famous selling point -- his first appearance, at the age of 25, was on May 4, 2002; he picked up the loss to Torii Hunter, Corey Koskie and the Twins. But don’t let his longevity fool you. At his best, Rodney was overpowering a closer as any in baseball: His 48 saves in 2014, at the age of 37, led the Majors. He’s still hanging around too, and he’s the only active player who was born in the 1970s. We just assume Rodney will still be around in 2029 as well. And he just got his first World Series ring.

7. David Robertson (NYY 2010-14, 2017-18, CHW 2015-17, PHI 2019)
Robertson was only a full-time closer for one year in New York and three years in Chicago, but this is a ranking of best relievers, not best closers. And Robertson has been one of the best every year of this decade, setting up Rivera for the first half of the decade and Chapman for a good part of the second half. He’s just always good. He’s not always appreciated -- he has made only one All-Star team -- but every team that has David Robertson is better for it.

8. Greg Holland (KCR 2010-15, COL 2017, STL 2018, WAS 2018, ARZ 2019)
The Royals were as fortunate as anyone in the closer sweepstakes, going straight from Holland to Davis. Holland was fantastic with Kansas City before missing the 2016 season recovering from the Tommy John surgery, but he returned to save 41 games for the Rockies in '17. He was a late signing out of Spring Training for the Cardinals in '18 and suffered accordingly, but since then, Holland has been outstanding for both the Nationals and the D-backs.

9. Tyler Clippard (WAS 2010-14, OAK 2015, NYM 2015, ARI 2016, NYY 2016-17, CHW 2017, HOU 2017, TOR 2018, CLE 2019)
Clippard is a pitcher who’s always a ton better than anyone appreciates, but no one ever notices because he rarely closes out games. He made two All-Star Games this decade, and he appeared in more games than any other pitcher. (No one is within 55 games of him, actually.) And if you’re into holds, Clippard leads in those for the decade as well. He even can be in the right place at the right time: He wasn’t on the postseason roster for the Astros in 2017 … but he still got a ring.

10. Mariano Rivera (NYY 2010-13)
Is it cheating to put him on this list? Absolutely it is: Rivera really only pitched three full seasons and isn’t in the top 10 of any major category for the decade. (He’s 22nd in saves for the decade.) But Mo was as amazing from 2010-13 as he was any other year of his career: He still had 44 saves and a 2.11 ERA in this final season, at the age of 43. You wouldn’t trust Rivera with the ninth inning in a big game still today? We would.

Honorable mention: John Axford, Dellin Betances, Steve Cishek, Mark Melancon, Andrew Miller, Darren O’Day, Jonathan Papelbon, Francisco Rodriguez, Huston Street, Tony Watson, Brad Ziegler