Michael Brantley, 2018-19 offseason
After 2018, the Yankees needed to get meaningfully better after JD Martinez, Alex Cora and the Red Sox wiped several different floors with them in what was supposed to be Year 1 of their championship window.
Instead, they patched holes with several different mid-tier targets and bullpen additions during an offseason we'll be discussing plenty later on.
By the end of 2019, though, it was clear the one-year wonder Red Sox weren't the team the Yankees should've been worried about. Instead, the Astros weren't going anywhere, and added contact-hitting/reliable Michael Brantley on a two-year, $32 million contract.
Year 2 of that deal ended up being significantly reduced by COVID, but in Year 1, the Yankees went back to the Brett Gardner well instead, using a ridiculous collection of fill-in left fielders as the year continued. Mike Tauchman and Cameron Maybin were very fun! Brantley hit .311 with 22 bombs and an .875 OPS/126 OPS+, knocking the Yankees out of the postseason. New York was an outfielder or two short all year, thanks to injury, while Brantley stayed healthy and mashed. It's not like the Yankees (and the juiced ball) didn't receive production from the position; Tauchman somehow matched Brantley (128 OPS+) in limited duty. But he got hurt and missed the postseason, then turned into a pumpkin in 2020 while Brantley stayed steady. Not the most egregious, but certainly a miss that left New York scrambling and coming up short.