In Game Seven of the American League Championship Series, Houston Astros manager A.J. Hinch called on Lance McCullers in the sixth inning to relieve starter Charlie Morton. In his four inning outing, McCullers threw his curveball over 75% of the time, and finished the game with 28 straight breaking balls. He completely shut down a potent Yankees lineup and paved the way for the Astros second World Series appearance.

McCullers is known to have a limited repertoire—a 94 mph fastball, a good changeup, and that tight bender—but he’s not unique on the Astros. As a team, they threw the fewest four-seam fastballs in the majors this season. It’s actually the third season in a row they’ve accomplished that feat. Charlie Morton threw his curveball almost 50% of the time in his five inning start in Game Seven, and almost 30% of the time during the regular season.

Under Jerry Dipoto, the Mariners have plotted a course in the direct opposite direction as the Astros. In an article about Erasmo Ramirez, I wrote this paragraph that is still relevant here:

“Over the last three years, the Mariners pitching staff has exponentially increased the number of fastballs they throw. In 2015, their pitchers threw a fastball around 37% of the time, a little bit above league average. This season, only the Rockies are throwing four-seam fastballs more often, and that’s largely due to their extreme home environment. The increased number of four-seam fastballs isn’t the sole reason for the Mariners pitching woes, but it’s certainly a factor.”

The Mariners ended up throwing the fifth most fastballs in the majors this season but it’s still a huge increase over a few years ago. As baseball moves towards a game dominated by power hitters and power pitchers, the most successful teams are moving away from the fastball. And the Mariners are getting left behind.

In July, Tom Verducci chronicled this change in pitching approach, focusing specifically on the Yankees. He interviewed New York Yankees pitching coach Larry Rothschild to get his perspective. Here’s what Rothschild had to say about fastballs in the modern game:

“Fastballs get hit. It’s amazing to me to see guys throwing in the upper 90s and they get hit. I don’t know how these guys do it. That’s how good major league hitters are. They have adjusted to velocity. To hit upper 90s, you have to gear up for upper 90s. So hitters are going up there to gear up for velocity. And when they do that, they can hit it no matter how hard you throw.”

This season, batters enjoyed a wOBA of .358 when hitting a fastball (four-seamers and sinkers combined), and that mark has increased year-over-year since 2014 when it was .333.

The Mariners pitching staff allowed a wOBA of .359 off their fastballs this year, 15th in the majors. All those additional fastballs from Felix Hernandez ended up really hurting him, as he allowed a .407 wOBA off his heater. Elsewhere in the starting rotation, James Paxton and Andrew Moore had excellent results off their fastball, while Nick Vincent and Emilio Pagan led the way in the bullpen—all four of those pitchers allowed a wOBA under .300 off their fastball.

If throwing more fastball isn’t the right approach for the Mariners, how did they perform when throwing other types of pitches? Below is a table listing the Mariners performance on the three major pitch type categories:

wOBA Allowed by Pitch Type Pitch Type % of Pitches wOBA MLB Rank Pitch Type % of Pitches wOBA MLB Rank Fastball 55.8% 0.359 15th Breaking Ball 32.6% 0.265 8th Offspeed 10.9% 0.338 28th

I was surprised to see how poorly the Mariners offspeed pitches graded out. It’s not a huge chunk of the pie, but it’s certainly not encouraging. More encouraging was their performance when throwing their breaking balls. Those pitches were actually quite effective. Many of the arms in the bullpen had particularly nasty breaking balls, which isn’t too surprising. Among the starting rotation, Paxton and Mike Leake had standout breaking balls. But the most surprising name was Ariel Miranda. He allowed a .233 wOBA off his slider in 2017, the 25th best mark for a slider thrown by a starting pitcher.

Throughout this offseason, I want to examine a few pitchers in particular—Miranda is an easy example—to see if throwing their fastball less often could be a benefit to them. Of course, shifting around pitch mix isn’t a cure-all solution. There’s a reason why traditional thinking has elevated the importance of the fastball. And throwing more breaking balls doesn’t come without greater risk of injury. But the game is changing and by encouraging pitchers to use their best pitch more often, whether or not it’s a fastball, better results could follow. With a staff full of pitchers without exceptional stuff in their repertoire, the Mariners need to start embracing different approaches to maximize their strengths. Throwing more and more fastballs isn’t necessarily the right approach.