Aroldis Chapman is quietly putting together a historic season

Several positive — and surprising — developments have helped push the Boston Red Sox into playoff contention this season. The Sox enter play on Friday with a 75-60 record, which gives them a 2.5 game lead on the first wild-card spot. Since trading Rafael Devers in mid-June, Boston has one of the best records in baseball behind only the Brewers and Blue Jays. 

Left-hander Garret Crochet has firmly planted himself in the AL Cy Young Award discussion. Crochet is leading the league in wins and strikeouts, while sitting third in ERA (behind Detroit's Tarik Skubal and Houston's Hunter Brown). Outfielder Roman Anthony has arrived and appears to be just as talented as scouts projected. His .865 OPS is second among rookies with more than 200 plate appearances, behind only the Athletics' Nick Kurtz. 

Meanwhile, at the back of the Boston bullpen, closer Aroldis Chapman is quietly having a historic season. 

The 37-year-old left-hander is putting up some of the best numbers of his career in his 16th MLB season after joining the Red Sox last offseason on a one-year, $10.75 million contract. Chapman has worked 52.0 IP on the year, collecting 26 saves with a 1.04 ERA and 0.673 WHIP. 

Chapman's 1.04 ERA translates to a 401 ERA+ -- a stat in which 100 equals league average, meaning he's been 301% better. Just three times in the history of the sport has a player finished a season with an ERA+ above 400: Robert Keyes (1944), Garnett Blair (1945), and Roy Parnell (1932). All three accomplished the mark while pitching in the Negro Leagues. 

Shane Bieber's 273 OPS+ in 2020 is the most recent instance where a pitcher was so significantly better than league average. 

Meanwhile, Chapman has allowed just 21 hits on the season, and only three of those have been home runs. Opponents are batting a mere .119/.183/.182 against him. He has walked 14 batters. 

Chapman's WHIP (walks plus hits per inning pitched) would also be the best mark in MLB history. George Walker posted a 0.734 WHIP in 1940. Pedro Martinez nearly matched it in 2000, with a 0.737 WHIP. 

Set to reach free agency again after the season, Chapman could parlay a historic season into another substantial payday even at this late stage in his career. Jon Heyman at the New York Post reported on Thursday that the team would like to bring him back for next season and the early indications suggest the interest is mutual.