https://blogs.fangraphs.com/red-sox-add-corey-kluber-to-rotation-of-question-marks/
Kluber... makes sense for Boston in a lot of ways, and indeed the two parties have been pretty frank about their mutual interest over the years. The two-time Cy Young winner has lost some velocity since his prime, but velocity was never his main weapon, and his spin rates remain above average, which helps his pitches retain some of their value. Thanks also to a still-effective cutter, changeup, and curveball, he’s able to entice hitters to chase and produce weak contact as well as ever. In 2022, he finished with 3.0 WAR in 31 starts for the Rays; for context, no Boston pitcher reached 2.0 WAR.
Kluber also happens to be elite in one facet of the game that sticks out among Boston’s acquisitions this winter. After Red Sox pitching finished 21st in walk rate last season, they appear to be intent on winning the walk battle in 2023. Kluber has allowed fewer than two walks per nine over his whole career; his career-best 1.15 BB/9 rate led all qualifiers last year (among pitchers with 50-plus innings, the leader was Martin at 0.80). Having Chris Sale and James Paxton back in the mix would add two more above-average control pitchers after the losses of Eovaldi and the still un-signed Michael Wacha.
Kluber’s ability to control his pitches was a big part of what made him effective in 2022. He worked the fringes of the zone all year, improving his Edge% from 40.8% in 2021 to 44.3%, good for the 15th-best improvement among 228 qualifying pitchers per Statcast. His called strike percentage also increased, from 16.7% to 18.3%, the ninth-highest rate among major league qualifiers. Outside the zone, he induced a 35.7% chase rate, ranking in the 96th percentile in the league, and in many cases, bad swings led to bad contact.
Another factor that led to Kluber’s productive 2022 was a change in approach against righties, who went from a .352 wOBA against him in 2021 to a .309 mark in ’22. He ramped up his use of the cutter against same-handed hitters, going from 21.6% to 34.6%, making it his most-used pitch — and it was his most effective, too, at 5.8 runs above average. But he also was able to limit the damage done by right-handers on his sinker by bringing it up and inside instead of trying to beat them down and away with it.
Right-hander Nick Pivetta is the only true holdover from the 2022 rotation, and he struggled to find a consistent rhythm last year. Sale’s last three-plus seasons have featured a truly terrible string of luck: Tommy John surgery, a bout of COVID, a fractured rib followed by a non-baseball medical issue, a fractured pinky finger on a comebacker in his second and ultimately final start of last season, and a bicycle accident resulting in a broken wrist. Paxton has yet to make his Red Sox debut after suffering a lat tear during his own Tommy John recovery last summer. After a promising rookie stint in 2022, there’s hope that 23-year-old righty Brayan Bello could earn a rotation spot for years to come, and the Red Sox have told 26-year-olds Garrett Whitlock and Tanner Houck to prepare to join the rotation, though the latter may be more likely to return to the bullpen with Kluber now in the mix.
That’s seven names, and if any five of them are pitching at or near their ceilings in 2023, they could make for a solid rotation. But each comes with his own concerns, and Kluber is the only one with even a 2.5-WAR season in any of the last three years. Red Sox fans will be holding their breath and crossing their fingers for good health.