When the Yankees signed Jacoby Ellsbury to a massive $153 million contract in the 2013 offseason, and then signed Brett Gardner to an extension months later, GM Brian Cashman obviously knew they were locking up two very similar players for the foreseeable future. Both hit for decent average, got on base, swiped bags, and played great defense. But they wouldn't offer a whole lot of power from the outfield, typically a major source of some serious offensive production (along with the corner infield spots). Even with that weakness, though, Cashman had to see their serious potential for success if they could provide elite defense and become a speedy, high OBP combo atop a lineup otherwise made up of power hitters.
Last year, the combination didn't work perfectly - Ellsbury had a decent, but not spectacular, year, hitting .271/.328/.419 with a 107 wRC+. Gardner also had a solid if not sensational season, hitting for a 110 wRC+ while playing decent defense in left. Neither of them had a bad year, but their inability to produce at a superstar level - which, while unfair to expect of them, is what it would've taken to drag last year's broken down Yankee squad to the playoffs - left the Yankees standing on the outside looking in come October. Also limiting their usefulness was Derek Jeter's stranglehold on the second spot in the order. This prevented Gardner from taking the spot many thought naturally fit him, relegating him to hitting much farther down in the order than a player of his talents would normally find himself.
With Jeter now enjoying retirement, though, 2015 has finally given these two players a chance to realize their combined potential. This season has seen Ellsbury and Gardner play just about as well as Yankee fans could've hoped, getting on base at a high rate while also swiping bases at a good clip. They're setting the table for the Yankee sluggers (who have been surprisingly productive in their own right), and this lineup has become far more dynamic than last year's anemic offensive squad. Not only are Ellsbury and Gardner playing like two of the best players on this team, they're actually two of the best outfielders in all the league through 36 games. Ellsbury is hitting .348/.419/.399 with a 134 wRC+ (which constitutes the best start of Ellsbury's career), and that .419 OBP is good enough for fourth in the majors among outfielders. His penchant for getting on base make Ellsbury an excellent leadoff man, but his speed makes him even more dangerous once he gets on base. Ellsbury is also near the steals lead among outfielders as well (second with 12 steals) - and guess who's right behind him? That's right - Brett Gardner has 10.
While Gardner's OBP isn't quite as good as Ellsbury's - although it's still .388, good for 11th among MLB outfielders - his higher slugging percentage of .447 makes Gardner a bit more suited to the second spot. Overall this year, Gardner is hitting .307 with a 135 wRC+ and already has three homers and seven doubles. This two-headed monster is exactly what Yankee fans have been waiting to see from these excellent outfielders, and while neither of them may be quite as good as all-world superstars like Bryce Harper or Giancarlo Stanton, having a pair of excellent, well-rounded players patrolling the warning track and hitting atop the lineup has given the Yankees one of the best outfields in the game. Ellsbury is 9th in the majors in fWAR among outfielders, and Gardner is 15th - the only other squads with comparably valuable outfielders in the early going are the Royals (Lorenzo Cain and Alex Gordon are tearing up the league so far), the Dodgers (Andre Either and rookie phenom Joc Pederson both have wRC+ ratings of over 170), and the Angels (Mike Trout remains amazing, but Kole Calhoun is having another good year, hitting .314/.363/.458 so far). Overall, that's not bad company at all for Gardner and Ellsbury to be in.
In addition to Ellsbury and Garder tearing up the league to start the season, the Yankees have also gotten a boost from fourth outfielder Chris Young. Young, who's managed to steal 90 at-bats from an old and ineffective Carlos Beltran, has already amassed 0.9 fWAR and is hitting .288/.352/.600. With the start Ellsbury and Gardner have gotten off to, plus Young's ability to compensate for the decline of Beltran, the Yankees have put together one of the most effective outfields in the game. While we all expected them to be good defensively, the offensive impact of Ellsbury and Gardner - and to some extent Young - has been the engine driving the 2015 Yankees. If they can continue getting on bases and stealing bases, the Yankees should remain one of the better offenses in the league.
Finally, in 2015, Ellsbury and Gardner have become the disruptive and devastating force - in the outfield, at the plate, and on the base paths - that we all hoped they could be when the Yankees teamed them up two offseasons ago.