How Bryan Woo unleashed a fellow Mariners ace just in time for the playoffs

This has been Bryan Woo's year. Posting a 2.94 ERA with a 3.47 FIP over 186.2 innings, he has risen to the top of the Mariners' rotation just two years after getting called up out of Double-A. While he won't end up taking home any hardware this year, he has put the rest of the American League on notice that he's one of the best starters around.

Just a few years ago, that was George Kirby. Called up in 2022, he placed sixth in Rookie of the Year voting and followed it up with a sophomore campaign where he pitched to a 3.35 ERA while leading all of MLB in BB/9 (0.9) and K/BB (9.05). It seemed like only a matter of time before he became a perennial Cy Young contender and ace of the star-studded rotation. Unfortunately, his fourth big league season has come with a few speed bumps.

His season started with right shoulder inflammation which kept him off the field until late May when, in his only two starts of the month, he gave up 11 earned runs and saw his ERA balloon to 11.42. It took him all the way until his 15th start to get his ERA below 4.00 for the first time on the season, after which he promptly conceded seven earned runs to the Mets. Needless to say, Kirby's 2025 was full of ups and downs.

George Kirby picked up a fancy new toy from his fellow Mariners ace

But the regular season is over now. The Mariners must turn their attention to the playoffs, where they'll get an extra few days to strategize against their first October opponent. With the shakiness of his season behind him, Kirby has turned to Woo for guidance. Ryan Divish of the Seattle Times recently reported that the two have been exchanging tips and tricks, which may have given Kirby a boost in his final start of the year.

Given the numbers, it makes sense that the sinker was a particular topic of discussion. This was the first season that Kirby's sinker was worth negative run value due to opposing hitters, who slugged .518 against what's meant to be soft contact pitch. Conversely, Woo's sinker was one of the best in MLB, accumulating a plus-nine run value while being his secondary fastball offering.

In Kirby's last start against the Dodgers, his sinker usage was 35.3 percent, a meaningful increase over his season average of 26.7. The pitch still wasn't quite as dominant as in years past but it had some highlight moments while, more importantly, helping to unlock his four-seam fastball which generated nine whiffs.

The timing couldn't be better for this exchange of knowledge to happen. Not only are the Mariners gearing up for the Division Series, there's still some uncertainty surrounding Bryan Woo's health after he sustained tightness in his pectoral muscle. And despite encouraging signs, the team can't align their rotation until they know exactly how he'll look against live hitters.

The last time George Kirby pitched in the playoffs, he was dominant, tossing eight scoreless innings, but that was during his outstanding rookie year. He has given us glimpses of that greatness this year, but has struggled to maintain consistency for any extended duration. However, with a few days to reset and a refined sinker, we could see him pitching at peak form as soon as this weekend.