Joe Girardi's use of the bullpen has steadily increased since the end of the 2012 season. The Yankees' 2012 campaign featured two starting pitchers, CC Sabathia and Hiroki Kuroda, who each threw for more than 200 innings. In addition, Phil Hughes pitched 191.1 innings, while Ivan Nova threw for a further 170.1. To put those numbers into perspective, Nova's 2012 innings were good for fourth most on the team, but would have led the 2015 Yankees (Sabathia led the team in innings pitched last year with 167.1).
Dellin Betances led Major League Baseball last year with 84 innings pitched in relief. Andrew Miller pitched an additional 61.2, accounting for 27% of the Yankees' bullpen innings last season. This year, the Yankees have added Aroldis Chapman to the mix, and are likely to rely on him for 55 to 60 innings after he has served his suspension to begin the regular season. Put together, the Yankees likely hope that the trio of Betances, Chapman, and Miller, constituting (on paper) the strongest back-end relief corps in the league, can combine for somewhere in the neighborhood of 200 innings pitched this season.
Where does that leave the Yankees in terms of aggregate bullpen usage for 2016? Last season, Yankees relievers pitched 530.2 innings, which was seventh most in MLB, and represented a roughly 6% increase from 2014. In both of these years, the Yankees utilized their bullpen at a higher rate than the rest of MLB, with bullpen usage defined as the fraction of a team's innings pitched by its relievers (see the figure below). The Yankees did not have a pitcher reach the 200 innings pitched threshold in either of those seasons, although Kuroda came close with 199 in 2014. Masahiro Tanaka finished second on the team in innings pitched with just 136.1 that year.
Given the upward trend in Girardi's use of his bullpen, and that it is more or less universally regarded as the strongest unit on the 2016 Yankees, it would be reasonable to assume that the Yankees are in store for even more bullpen innings this year. Despite the signs pointing in this direction, do not be surprised if the Yankees' bullpen usage levels off in 2016 or even declines.
One factor in a potential leveling off or decline concerns the Yankees' starting pitching. Michael Pineda has publicly stated his goal of reaching 200 innings this year (he pitched 160.2 in 2015), and the Yankees are hoping that Nathan Eovaldi can come closer to the 199.2 innings he pitched for the Miami Marlins in 2014 (he threw 154.1 in his first season with the Yankees). The Yankees have not had two starters contend for 200 innings since 2012, when Girardi used the bullpen for just under 31% of the Yankees' innings.
A second factor is the lack of proven commodities behind Betances, Chapman, and Miller. Chasen Shreve had a great start to 2015 but struggled mightily down the stretch. Johnny Barbato and Luis Cessa are unproven at the Major League level, and Nova is unproven as a reliever.
The 2016 Yankees are built to win with their bullpen, which arguably employs three of the top ten relief pitchers in MLB today. But even if the bullpen leads this season's charge for a playoff spot, they may spend less time on the mound if Eovaldi and Pineda can evolve into the innings-eaters that the Yankees have sorely lacked over the past few years.