Click here to see the rest of the best bullpens for each decade since the 1960s.
You might think bullpens haven't changed much since 2010, but there have been subtle shifts. The seven-man bullpen is now de rigueur, with teams often employing eight relievers at a time. With so many relievers to choose from, the number of pitchers used per game has increased from 3.87 per game in 2010 to 4.11 in 2015. With that comes even shorter stints and less usage for closers. Jonathan Papelbon has pitched 70 innings in a season just once in his career -- hitting 70 on the nose in 2012. Craig Kimbrel pitched 77 innings as a rookie but hasn't topped 67 since and has averaged just 60 innings the past two seasons.
But the biggest change has come in the pure dominance we see from so many relievers. More relievers than ever throw 95 mph; combined with the expanded strike zone and the general increase in strikeouts, strikeout rates for relievers are sky high. Look at strikeouts per nine innings by relievers over the past 20 years:
Here are the number of relief seasons per decade in which a pitcher threw at least 50 innings and averaged at least 10 K's per nine (at least 80 percent of appearances coming as a reliever):
We're only six years into this decade and have already obliterated the total from the 2000s. And here are the number of relief seasons where a reliever pitched at least 50 innings with an ERA under 2.00:
Again, we're on the way to shattering the total from the 2000s. In 2015, 13 relievers accomplished this feat.
We've had many dominant bullpens this decade, so it wasn't easy picking my three best. Here they are:
1. 2015 Kansas City Royals (95-67): 30-14, 2.72 ERA, 56 saves, 73-3 when leading after seven
The Royals have had dominant bullpens for years and it's not obviously clear that 2015 was the best one:
2012: 25-21, 3.17 ERA, 8.6 K's per nine
2013: 33-24, 2.55 ERA, 9.6 K's per nine
2014: 28-18, 3.30 ERA, 8.7 K's per nine
2015: 30-14, 2.72 ERA, 8.4 K's per nine
The 2014 pen had the best trio in Greg Holland, Wade Davis and Kelvin Herrera but the highest ERA; the 2013 pen -- when Davis was still in the rotation most of the year -- actually had the lowest ERA and highest strikeout rate; the 2015 pen, even as Holland struggled at times and eventually blew out his elbow, still lost just one game it led all season heading into the ninth. Overall, the 2015 pen was a little deeper than 2014 thanks to Ryan Madson, Luke Hochevar and Chris Young ... and, of course, helped win a little thing called the World Series.
2. 2012 Baltimore Orioles (93-69): 32-11, 3.00 ERA, 55 saves, 74-0 when leading after seven
Certainly the most clutch bullpen of the decade. The Orioles had that perfect record after seven innings -- although they did lose one game they led heading into the ninth inning -- and they went an amazing 16-2 in extra innings. Their top five relievers all threw at least 55 innings and the highest ERA was 2.64. That group of closer Jim Johnson plus Darren O'Day, Pedro Strop, Troy Patton and Luis Ayala may not have been the most statistically dominant when it came to strikeouts -- only O'Day averaged more than one per inning -- but they got the job done all season. Heck, even Chris Davis was pressed into one 17-inning game as a reliever -- and threw two scoreless innings to get a win.
3. 2012 Atlanta Braves (94-68): 25-14, 2.76 ERA, 47 saves, 78-2 when leading after seven
The 2013 Braves own the lowest bullpen ERA of the decade so far with a 2.46 mark, but that club blew four games in the ninth. This team was 83-1 when leading after eight as Kimbrel had his best season, going 3-1 with 42 saves, a 1.01 ERA and 116 strikeouts in 62.2 innings. He allowed just four extra-base hits the entire season. His support group included Eric O'Flaherty (1.73 ERA in 57.1 innings), Chad Durbin (3.10 ERA in 61 innings), Jonny Venters (3.22 ERA in 58.2 innings), Cristhian Martinez (3.91 ERA in 73.2 innings), Kris Medlen (2.48 ERA in 54.1 innings) and Luis Avilan (2.00 ERA in 36 innings). The Braves lost the wild-card game 6-3 to the Cardinals, as Medlen, now in the rotation, allowed five runs (three unearned as the Braves made three errors) in 6.1 innings. Kimbrel didn't get into the game until the ninth inning, when the Braves were down by three runs.
Proving a great bullpen can easily be wasted if the starting pitching, defense and offense don't do their jobs. Or the manager refuses to use his best reliever in a more clutch situation.