2018: James Paxton
Everybody wishes the James Paxton trade worked out. It was exciting at the time, and he possessed a top-of-the-rotation profile the Yankees desperately needed alongside Severino and Masahiro Tanaka. The only problem? He could never stay healthy ... something Cashman knew and still decided to roll the dice on.
We'll forever remember Paxton for buzzsawing the Red Sox in that incredible 2019 outing at Yankee Stadium, as well as his ALCS showing against the Astros (8.1 innings, 2 ER, 12 K) ... but injuries limited him in 2019 (only 150.2 innings pitched) and he eventually succumbed to Tommy John surgery in 2020 (only five starts and a 6.64 ERA). He's now a member of the Red Sox, but has yet to pitch due to more injuries.
Anyway, at the time of the trade, Paxton had never made more than 28 starts in a single season. In fact, he only had three years where he made 20 or more. And guess who was in this deal going back to Seattle?! Justus Sheffield, who the Yankees wouldn't trade the year prior for Machado! One of the other prospects? Erik Swanson, who's now a member of the Blue Jays after they bought high on the right-hander following a 1.68 ERA, 1.84 FIP and 0.91 WHIP year in 2022. That should work out well for New York, right?
Paxton came with high expectations and left with a whimper. It really was a shame he couldn't stay healthy at any point in his career, but the Yankees ignoring that important tidbit has this deal higher up on the list than it should be.