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The New York Yankees excellent bullpen

The New York Yankees bullpen has been excellent in its first year post-Mariano Rivera. Here's a closer look at their success.

Anthony Gruppuso-USA TODAY Sports

After 17 straight seasons of having Mariano Rivera anchor the bullpen, the New York Yankees bullpen started the season with a different closer for the first time since 1997. Thus far, only the Atlanta Braves bullpen has a higher strikeout rate than the Yanks 27.7 percent and only the Boston Red Sox have more fWAR than their 2.5. Steamer projected just 1.2 fWAR from the Yankees bullpen going into the year (all stats entering Monday).

Besides David Robertson, who was the heir apparent to Rivera's closership, the Yankees bullpen did not feature well-known names. Besides a strained groin which sent him to the DL, Robertson's succession has been smooth. He's saved 10 of 11 games with nine shutdowns and two meltdowns. In 14 appearances, he has strikeout and walk rates of 39.6 percent and 5.7 percent, respectively.

The right-hander started using a cutter in 2011, and he's steadily increased it's usage. Now, he throws his four-seam fastball on just 10 percent of his pitches, while relying on his cutter on 56 percent of his pitches and using his devastating knuckle curve the rest of the time.

Speaking of knuckle curves, Dellin Betances has been unhittable. At 1.05, the 6'8 right-hander owns the lowest xFIP in baseball by more than seven-tenths of a run. The sum of his ERA, FIP and xFIP is lower than Gerrit Cole's ERA. Batters are missing his knuckle curve on more than 60 percent of their swings. When they're not swinging and missing, Betances is dropping the pitch into the strike zone. Overall, batters are swinging at the pitch more frequently when it is outside the strike zone than when it is in the zone, a remarkable feat. Since transitioning to the bullpen last season, the big right-hander has ditched his ineffective third and fourth pitches, and added fastball velocity, making him a strikeout machine.

Between the two of them, Robertson and Betances have recorded a much higher rate of looking strikes and looking strikeouts than the average major league pitcher. In most cases this would be sign of coming regression for their strikeout rates, as swinging strikes have a higher correlation with strikeout rate than looking strikes. As a team, the Yankees relievers have a 10.4 percent swinging strike rate, which is the 16th best mark in baseball. It's on par with the Cincinnati Reds, who possess a strikeout rate almost seven percentage points lower.

However, Robertson has maintained a low swing rate throughout his major league career, thanks in large part to his knuckle curve. As mentioned above, batters are taking Betances' knuckle curve for strikes and swinging when it's outside the zone. Combine the knuckle curves with a good framing catcher such as Brian McCann, and you get a recipe for backwards Ks. Curveballs have the lowest swing rate of any pitch, and batters are particularly loath to offer at the benders utilized by Robertson and Betances.

It's not just Robertson and Betances. Adam Warren has strikeout and walk rates of 25.2 percent and 6.1 percent. He's juiced up his fastball to 93.7 miles per hour while swapping out most of his two-seamers for sliders. The slider is getting hitters to chase, and they have a contact rate under 50 percent when they do so. Matt Thornton is still firing bullets at left-handed hitters and Shawn Kelley has maintained his impressive strikeout rates from 2013 until a back injury sidelined him.

Going forward, Steamer isn't a big believer in the Yankees relievers (see what I did there). It likes Robertson, and it thinks Betances has improved, but not nearly to this extent. The rest of the bullpen projects as roughly replacement level. While it's a long shot for Betances in particular to keep pitching this well if only because his numbers are so outlandish, his Steamer projection is heavily informed by high walk rates from his starting days. After all, projecting 50 and 60 inning samples is very difficult for the simple reason that almost anything can happen in that frame. The Yankees probably don't have the second best bullpen in baseball, but relief pitchers can surprise you like that.

It's a new look for the Yankees. Their offense is mediocre, and their best infielder is Yangervis Solarte. Some days the combined age of their middle infielders is 75. At the end of the year, Brett Gardner might lead the position players in fWAR. They're AL East contenders thanks to their starting pitching (read: Masahiro Tanaka) and a bullpen that has been excellent. With a lineup that features Alfonso Soriano in the middle of the order, their relief pitching might be more exciting than their offense.

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Stats courtesy of Fangraphs, Brooks Baseball and Baseball Savant

Chris Moran is a former college baseball player and current law student at Washington University in St. Louis. He's also an assistant baseball coach at Wash U. In addition to Beyond The Box Score, he contributes at Prospect Insider and Gammons Daily. He went to his first baseball game at age two. Follow him on Twitter @hangingslurves