The biggest question mark over the New York Yankees heading into the past offseason was the lack of a starting shortstop. Brian Cashman had no viable candidates in-house, and precious little on the open market, leading him to swing a trade out of the team's nonexistent starting pitching depth to add Didi Gregorius. Two weeks later, the rotation hole was plugged with another trade, this time for Nathan Eovaldi. Out went Shane Greene, Martin Prado, and David Phelps; in came Gregorius, Eovaldi, Garrett Jones, and right-handed pitching prospect Domingo German.
All-told, it appeared a very reasonable pair of trades for two talented then-24 year olds with big league track records. Now, it looks a veritable haul with Greene, who might have appeared the most valuable piece being shipped out, being demoted to Triple-A for the second time this year, having previously been moved to the bullpen. Prado is still useful for his versatility despite a 85 wRC+, but is a potential waiver-wire trade candidate for the cost-cutting Marlins. Phelps has largely been pitching out of the rotation for the same Marlins, but would have likely remained a swingman relegated to long relief with the Yankees.
Of course, even at a low cost, the deal could only be as good as the production of Eovaldi and Gregorius, and early in the season both scuffled. Gregorius more visibly so as the everyday player; an appalling 37 wRC+ in April as he struggled defensively at shortstop. Eovaldi was less completely unplayable, but largely inconsistent, culminating in a blow-up against his old Miami team in mid-June when he couldn't get out of the first inning. That left him with a 5.12 ERA (128 ERA-) and 4.05 FIP (99 FIP-).
The Yankees stuck with both though, perhaps due to a lack other options to some extent, but the team is now reaping the benefits of letting two young players work through their struggles. Gregorius has gone back to being the type of defensive asset he was expected to be, but the bat has come around as well with him being a league-average hitter (100 wRC+) since the start of June. Eovaldi has pitched to a 72 ERA- and 75 FIP- since his implosion against the Marlins. Both their strong second halves have picked up the overall body-of-work on the year; Eovaldi's 2.1 WAR has him second on the team among starting pitchers while Gregorius' 1.4 WAR is as much as Jacoby Ellsbury and Carlos Beltran combined.
Eovaldi is demonstrating the effect a change in pitch arsenal can have, as the split-finger fastball he has added this season is now the reliable third weapon which has helped him greatly cut-down on his hits allowed. Larry Rothschild has helped him add the pitch and continued to work with him in tweaking the delivery, now with apparent success. Meanwhile Gregorius has apparently benefited from major league coaching as well, as assistant hitting coach Alan Cockrell talked about helping Didi shorten his swing back in June. It's likely no coincidence that Gregorius has since been having a lot more success spreading the ball to all fields, rather than the more pull-heavy approach earlier in the season which was never suitable for a non-power hitter.
Obviously it is never a guarantee that a young player can turn it around at the major league level, even with the help of big league coaching. For players with potential though, there is the possibility that given the time and opportunity to succeed, and aided by patience, they can develop into assets for a contending team. Crucially for the Yankees, Eovaldi and Gregorius have seemingly done just that, and will need to keep producing if the Yankees are to remain in first place in an increasingly tight American League East.