MLB’s Best Reliever in 2021

Since the retirement of Mariano Rivera in 2013, the MLB’s best reliever has been a few different pitchers. Craig Kimbrel, Andrew Miller, Kenley Jansen, Zack Britton, and Aroldis Chapman all come to mind. Through 2021, the best reliever in baseball has by far been New York’s Aroldis Chapman. Not only is he dominating his fellow relievers in every stat, but he is making his own unique argument for a chance at the Cy Young award. Chapman ranks 11th in WAR for all pitchers, which is unheard of for a reliever this early in the year. The Cuban Missile is throwing his four-seam less, and his sinker more, and the results are superb. If Chapman can keep these numbers up, he might just break baseball. 


Statistics are not everything, but boy are Chapman’s impressive. The MLB’s best reliever has an ERA of 0.00. In 18 innings, Chapman has not allowed a single run at the time of writing, which is ridiculous. ERA is not the end-all-be-all stat, but more advanced statistics back up his dominance. The former Red and Cub’s FIP is 0.32, and was in the negatives just a few games ago. For reference, the best ever FIP for a qualified pitcher in a season is 1.287 back in 1908. Although Chapman does not pitch enough innings to qualify for that record, it is a good example of just how dominant he has been this season. At one point this season, Chapman’s FIP was negative, which should not even be possible. With just 5 hits and 0 runs allowed on the year, you would be shocked to hear that there’s more. 

Everyone knows about Chapman’s historic strikeout numbers in the past, but 2021 has brought upon a whole new level of dominance. The left-hander is striking out 2 batters per inning so far this year for a K/9 of 18.0. So far in his 11-year career, his highest K/9 ever recorded is 17.7, which is also the highest ever single-season number logged. No pitcher has been able to hold onto the ability to strike out 2 batters an inning for a full season, but Chapman might just be able to do it. It will be interesting to see if the 6x all-star will continue to hold these astronomical numbers all season. Yet anybody is able to break down and marvel at the closer’s numbers, let’s break down why he has been so dominant. 

A New Style of Pitching 

The 6’4 220-pound Chapman is well known for his explosive triple-digit fastball. However, his 2021 fastball is up a full mile an hour from his past two seasons. Over the past two seasons, the Cuban Missile has also been developing a splitter which is just devastating. It has only been put in play once all year and makes opponents whiff almost two-thirds of the time. Adding a third off-speed pitch to go along with his sinker and slider has proven beneficial to the big lefty, as he no longer needs to solely rely on his fastball. He is throwing the fastball almost 20% less than normal, and it is making hitters look silly. The sinker is still his strikeout pitch though. It consistently sits above 100 MPH, and has been a strikeout pitch 15 of the 27 times it’s been thrown. 

Is throwing more off-speed a good thing for a flamethrower? For Chapman in the past, the answer has been no. Yet in 2021, he seems to have much more control over his secondary pitches, and they look more developed. His slider is breaking 3 more inches than in past years, and it is making hitters struggle to barrel up pitches. It will be interesting to see how long to MLB’s best reliever can stay so dominant. Let’s look at the rest of the season. 

Playoff Inconsistencies 

It is pretty well-known that Chapman has let up some very important playoff homeruns in the past. In fact,the Rajai Davis homerun he allowed

was the fourth-highest Championship win probability play of all time. Despite all his regular-season success, the MLB’s best reliever has been labeled as a playoff short comer. This might just be an exaggeration. Although Chapman has allowed some iconic home runs, such as Rajai Davis and Jose Altuve, but he has been good in the playoffs. His ERA is 2.40, which is not Mariano Rivera good (0.70), but is solid, nonetheless. 

 In 2021, Chapman is playing on a talented, but struggling Yankees team that is pushing for the playoffs. The fans of New York are not only hoping that Chapman can continue his regular-season success, but that he can continue to keep on the legacy of the first ballot hall-of-famer in Rivera. If the Yankees can get back to the World Series for the first time since 2009, they will be heavily relying on the flamethrower. So far in 2021, the MLB’s best reliever has been Aroldis Chapman, who is looking to prove his doubters wrong. 

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