When an ace expands his repertoire, it can make the game's nastiest pitchers even nastier. That's exactly what's happening with these pitchers in 2021.

Multiple big-name pitchers around the league have either introduced an entirely new pitch this season or are throwing a formerly little-used pitch a lot more than they were before. And it's more than just raw frequency -- they're using those new pitches to rack up K's.

Here are four star pitchers with a new strikeout pitch in their arsenal in 2021.

Gerrit Cole, Yankees -- Changeup
The numbers: 15% usage, 89.3 mph, .155 AVG (9-for-58), 21 K

Cole's formula for strikeouts over the last three seasons, starting from when he joined the Astros in 2018, was simple: elevated four-seamers, sliders and curveballs down and away. The right-hander struck out more batters, 696, than anyone else from 2018-20; 95% of those strikeouts came on four-seamers, sliders or knuckle-curves.

Cole would throw a changeup or two every now and then, but he was barely using the pitch -- his changeup usage over those three seasons was just under 6%. He had 23 strikeouts total on changeups, out of the 696.

But this year? The changeup is in. Cole is throwing it 15% of the time, nearly tripling his usage from 2020 to '21. And he's using it to get strikeouts. Cole has 21 strikeouts on changeups, which is already the most strikeouts he's had on changeups in a single season in his career.

Cole's changeup usage and K totals, since 2018
2018: 4.5% usage | 5 K
2019: 7.4% usage | 13 K
2020: 5.6% usage | 5 K
2021: 14.8% usage | 21 K

From 2018-20, when Cole had two strikes on a hitter, he threw them a changeup only 5% of the time. In 2021, he throws two-strike changeups 17% of the time, and it's working.

He's not the only Yankees pitcher who's utilizing his offspeed stuff more this season -- two other notable examples are Corey Kluber, who was implementing a similar change before he got hurt, and Aroldis Chapman, who's regularly throwing a new splitter now.

Tyler Glasnow, Rays -- Slider
The numbers: 32% usage, 87.4 mph, .193 AVG (11-for-57), 14 K

There was a lot of hype about Glasnow developing a new cutter/slider hybrid pitch heading into the season, because the Rays right-hander was already so dominant as a two-pitch power pitcher. The idea was that Glasnow's fastball-curveball combo was enough for him to rack up strikeouts on its own, but finding a third effective pitch could even take him to another level.

Now that he's using it in real game action, Glasnow sure seems like he's found what he was looking for. He's throwing his new slider almost a third of the time, and more than twice as often as he's throwing his curve.

He uses each breaking pitch to attack hitters in a specific way. Glasnow attacks the strike zone with his slider; he throws it within the zone or on the edges 59% of the time. His curveball, on the other hand, he buries below the zone; it's a chase pitch 56% of the time.

The curve is still Glasnow's primary strikeout pitch -- he has 56 strikeouts on curveballs, more than he has on fastballs (47). But his slider is getting K's too -- 14 of them so far.

Compare that to the changeup that he would mix in as a third pitch once in a blue moon over the last couple of seasons, before he had the slider/cutter; Glasnow had a grand total of zero strikeouts on that changeup from 2019-20.

Brandon Woodruff, Brewers -- Curveball
The numbers: 13% usage, 83.8 mph, .111 AVG (4-for-36), 15 K

Woodruff has slowly worked a curveball into his repertoire since 2018, and now it's finally paying off as a major weapon for the Brewers ace in his best season yet.

Woodruff's curveball usage has increased every year; he's gone from not throwing a curve at all in his debut in 2017 to now throwing it just over 13% of the time. That's double the amount he was throwing a year ago.

Woodruff's curveball usage by season
2017: 0%
2018: 0.8%
2019: 1.9%
2020: 6.4%
2021: 13.3%

Along with that increased usage have come results. Woodruff's best pitch is still his overpowering four-seam fastball, but his curveball is now the pitch that he's getting the next-most strikeouts with.

The key is that he's getting a lot more movement on his curveball than ever before, especially vertical break.

Woodruff's vertical movement by season, overall vs. avg.
2018: 44.7 inches of drop | -9.5 inches below avg.
2019: 43.5 inches of drop | -8.3 inches below avg.
2020: 49.3 inches of drop | +0.9 inches above avg.
2021: 53.2 inches of drop | +4.8 inches above avg.

He's also throwing it harder -- Woodruff's curveball velocity has increased every year, too, from 79.3 mph in 2018 to 81.2 mph in '19 to 83.5 mph in '20 to 83.8 mph in '21. A harder curveball with sharper movement -- no wonder Woodruff is getting all those K's with it now.

Marcus Stroman, Mets -- Splitter
The numbers: 13% usage, 86.6 mph, .184 AVG (7-for-38), 12 K

Stroman unveiled a new split-change in Spring Training, a pitch he learned from Mets teammate Robert Gsellman when they were rehabbing together in Brooklyn last summer. It looked nasty then, and it looks nasty now that he's using it in the regular season.

The right-hander is throwing the split-change a little over 12% of the time, which is more than he's ever used an offspeed pitch -- he used to throw a normal changeup but was throwing that one only around 5% of the time.

There's a reason Stroman is throwing the split a lot more than he used to throw the change. It's proving to be a highly effective pitch. Opposing hitters are whiffing on over a third of their swings against it, and when Stroman throws it with two strikes, it puts the hitter away almost a third of the time.

Stroman's 12 strikeouts on splitters this season alone are basically as many as he had on changeups from 2017-19 (13 changeup K's). It's also been the best ground-ball pitch this season for a notable ground-ball pitcher -- Stroman's split-change is generating a 63.0% ground-ball rate on the batted balls against it, his highest ground-ball rate on any pitch type.