On July 25, Masahiro Tanaka reached the nadir of his season. Pitching at Fenway Park, the Yankees' top starter surrendered 12 runs to the Red Sox while recording just 10 outs, exiting in the middle of the fourth inning.

With the Yankees in a funk at the time, Tanaka's season could have spiraled. Instead, the right-hander has found a new gear and improved his signature pitch to move back to his old, reliable self in the last month.

In six starts since then, Tanaka has thrown 36 2/3 innings and allowed just three homers and 14 runs, good for a 3.44 ERA. Opposing batters are hitting just .241/.281/.416 against him, and he's struck out 26 to just eight walks. The Yankees have won all but one of those outings, and Tanaka has pitched into the seventh inning or later three times.

Key to Tanaka's turnaround has been his splitter. Since he joined the Yankees in 2014, he has had by far the best splitter in baseball according to Fangraphs' pitch values. He's consistently thrown it between a fourth and fifth of the time, and the offering had acted like a security blanket, a go-to offering for swings and misses ... until this season.

In 2018, Tanaka had a .210 batting average against on his splitter with a .318 slugging percentage. This season, that skyrocketed to .274 and .438, respectively, as hitters began to square up the pitch in ways they hadn't before.
As detailed in Lindsey Adler's article on The Athletic, Tanaka knew he had to make adjustments after that aforementioned start in Boston.

With reported changes to the baseball, including lowered seams, the 30-year-old's repertoire was adversely changed and he sought a new grip to the splitter with pitching coach Larry Rothschild.
"I don't want to make any excuses," Tanaka told Adler. "As a player, I feel I need to be able to adjust to what we're given to play with. Either you go ahead and adjust, or you wait until they make an adjustment to the ball. I was like, 'No, I'm going to be the one to make an adjustment.'"
Tanaka had shelved the splitter at times due to its ineffectiveness going into the Boston outing. Since then, with alterations to his grip and movement, he's throwing it more than any other pitch in August. Better yet, it's returned to pre-2019 levels of success with a .229 average against, .333 slugging percentage and no home runs against the pitch. It hasn't gotten quite as many swings and misses, but the offering's been a worm-killer by generating plenty of ground balls.
Here's the thing: Tanaka, outside of that Boston start, has been effective this season. Very effective at times, including a three-hit shutout of the Rays in June.
So what was he doing without his signature splitter? That's easy: Relying increasingly on his slider.
The slider has been a similarly successful pitch for Tanaka, and it turned into his new go-to offering before alterations to his splitter.. Opposing hitters have batted just .189 against it and whiffed on a third of their swings. While he's regained confidence in his splitter, he hasn't lost any in that slider, throwing the pitch 42 times in his seven shutout innings against the Mariners on Tuesday.

With two strong offspeed pitches, Tanaka goes right back to the front of the Yankees' rotation. Though any player can slump, the right-hander now has two nasty pitches to depend on, feeding hitters a steady diet of offspeed. The slider moves horizontally, the splitter straight down, and hitters' success has sunk against the splitter as he subverts their expectations.

Tanaka had a similar slump in 2017 before finding his groove before season's end. That culminated in an impressive finish to the regular season and a stay as the Yankees' ace in October. Coupled with James Paxton's undefeated August, the right-hander gives the Yankees what they needed -- a salve to a rotation that's been affected by injuries. 

Of course, there will be more adjustments ahead for Tanaka as hitters react to yet another change in his pitch selection. With more weapons in his control, though, this recent success portends a better end to his season, and thus more opportunity for the Yankees.