Can you name the starting pitcher with the lowest ERA in the month of May this year? If you paid attention to the Pitcher of the Month awards announcements yesterday, you might know the answer. If you’ve been paying attention to Major League Baseball at all over the past five years, you can definitely guess it. The answer, to nobody’s surprise, is Clayton Kershaw, who posted a ridiculous 0.91 ERA over six starts. What’s infinitely less intuitive and more thought-provoking is the identity of the pitcher who is second on the May ERA leaderboard: CC Sabathia.

In the interest of full disclosure, a bit of leaderboard manipulation is necessary in order to find Sabathia’s ERA ranked ahead of every pitcher not named Kershaw. A groin strain sent Sabathia to the disabled list after his start on May 4th and limited him to just four starts and 26 innings pitched for the month. So, if we’re being technical, Sabathia’s 1.04 ERA was second in the majors among starting pitchers with a minimum of 20 innings pitched. But the arbitrary nature of month-long splits isn’t why we need to talk about Sabathia. We need to talk about Sabathia because that great month contributed to his ERA doing this:

Sabathia closed out his 2015 season with a 2.86 ERA over his final nine starts. The difficulties he experienced off the field — and which immediately followed that impressive run — have been well-documented and are outside the scope of this analysis. Let’s focus entirely on what we know has happened on the field, which is that Sabathia has picked up right where he left off, recording a 2.85 ERA through his first eight starts of 2016. Considering Sabathia turns 36 years old next month and is coming off a disappointing three-year stretch during which he posted a 4.81 ERA, there are two obvious questions here. First: how did this happen? And second: will it last?

Let’s start with the “How?” first because it’s the most interesting and it’s always nice to start with the good news. The biggest problem Sabathia has faced in recent years – velocity decline – is not a secret. It’s the same problem every power pitcher faces in his 30s. A common difference between elite power pitchers who make the Hall of Fame and those who flame out after age 30 is the ability to successfully adjust when that inevitable velocity decline occurs. Unfortunately for Sabathia, he’s struggled to find the right adjustment.

One thing aging fastball pitchers will try is the increased usage of a two-seamer or sinker – if you can’t blow your four-seamer past batters anymore, you might as well try to induce weak contact with a pitch that moves, right? Starting in 2014, Sabathia adopted that approach.

CC Sabathia Fastball Usage Year Four-seam% Sinker% 2012 40.0% 14.3% 2013 42.8% 14.5% 2014 27.4% 29.5% 2015 28.3% 30.2% SOURCE: Brooks Baseball

It was a reasonable enough plan but, as his struggles since 2013 indicate, the positive results never arrived.

This year, he’s made an adjustment that’s even more drastic. Sabathia is still using his sinker, but the four-seam fastball that was the centerpiece of his repertoire for so long has been scrapped and replaced with a cutter. Sabathia’s status as a Yankee means that during Spring Training he was even able to consult with a man who is arguably the world’s foremost expert on pitching with a cutter: Mariano Rivera.

Sabathia is hardly the first pitcher to adopt a sinker/cutter approach in his later years. There might not be a sinker/cutter repertoire more famous than the one employed by Roy Halladay during the second half of his career. More recently, Dan Haren was the king of late-career cutter usage before retiring this past winter. According to research by Ben Lindbergh, the cutter is the most common new pitch for a major-league pitcher to add during his career. Sabathia is traveling a well-trodden path and it’s hard to deny that the the results for Sabathia so far have been anything but encouraging.

The biggest thing the cutter has done for Sabathia this season is bolster his repertoire against right-handed batters. He’s using the pitch against righties and lefties both, but against righties it’s become his most used pitch. His usage of the pitch against righties per Brooks Baseball: 33% overall, 37% when he’s ahead in the count, and 40% with two strikes. With his new pitch in tow, his struggles against right-handed batters have dissipated.

Right-Handed Batters vs. Sabathia Year wOBA 2013 .347 2014 .401 2015 .370 2016 .271

It’s worth noting that this is not a BABIP-fueled small-sample creation. His K%, BB%, BABIP, and batted-ball rates against righties are all within typical ranges for him with one key exception to which we’ll get in a moment. As for the cutter itself, righties are hitting .234 against the pitch while slugging just .319.

Sabathia’s results overall are nearly as impressive. Unsurprisingly, his current 2.85 ERA is the second-lowest mark of his career after the 2008 season (2.70 ERA), itself famous for his post-trade run with the Brewers. But ERA isn’t the only indicator that Sabathia is getting improved results. He’s allowing fewer base-runners (1.20 WHIP) than he has since 2012 and his 3.18 FIP is his lowest since 2011.

The sinker/cutter approach hasn’t resulted in a significant improvement to his strikeout and walk rates — in fact his 8.2 BB% is well above his rate in recent years — but early results suggest that he is achieving the positive result of inducing weak contact. After posting a consistent soft contact rate near 16% since 2012, that figure has jumped to 23.4% this season. He’s also keeping excellent company on the exit-velocity leaderboard:

Finally, it’s time to get to the more important question: “Will it last?” Which means it’s time to mention the one statistical category that jumps in stat that’s a definite candidate for regression: his home-run rate. His 4.0% HR/FB ratio is the third lowest among starters (min. 40 IP) this season and is less than half his career HR/FB ratio of 9.7%. Although it certainly stands to reason that moving away from the four-seamer may result in fewer home runs allowed by Sabathia this season, a drop this extreme is unlikely to be sustainable, particularly when taking his home ballpark into consideration.

The fact that his strikeout, walk, and ground-ball rates are all essentially unchanged and his home-run rate screams that regression is coming makes it hard to buy into New Sabathia as a true sub-3.00 ERA pitcher. That’s not to say, however, that the improvements he’s made aren’t real. If his cutter allows him to sustain his newfound effectiveness against right-handed batters it will go a long way to helping him return to being a productive major-league starting pitcher. As with any significant changes for a pitcher, the real test will be to see whether hitters are able to adjust to Sabathia’s new approach as they get multiple looks against him.