CC Sabathia's success against lefties should make Ivan Nova the Yankees' fifth starter

The fifth starter debate for the Yankees will come to an end at some point between now and April 4 with much of that debate focusing on whether Ivan Nova or CC Sabathia is better poised to perform as a starter this season. One recent PSA take argued that Nova should emerge from this competition victorious, despite Sabathia's $25 million salary and his stature as a team leader, Cy Young Award winner, and World Series champion. The argument is well-reasoned and represents a particular approach to answering the fifth starter question, namely, who is the better positioned to be successful as a starter at the season's outset.

An alternative approach to answering the fifth starter question begins with the assumption, which is almost certain to occur, that both Nova and Sabathia will be included on the Yankees' Opening Day roster. Given that this is the case, and that one will be a starter and the other a reliever, another approach would be to consider how to optimize the innings between the two. Nova may indeed be the better choice for a starter, but if he is also the better candidate to relieve, the Yankees will need to try to project the benefit the get from Nova as a reliever against the loss they incur from having Sabathia come out of the bullpen rather than Nova.

Because both Nova and Sabathia have pitched primarily as starters to this point in their careers, projecting their performance out of the bullpen is far from an exact science. Three areas that the Yankees coaching staff and front office might choose to look at in making this projection are how their respective pitch repertoires project to the bullpen, their recent track record against same-handed batters (righties against Nova and lefties against Sabathia), and their recent track record with runners on base.

Pitch Repertoires

Nova's repertoire already resembles that of a reliever in that he is mostly a two-pitch pitcher, fastball and curveball, while mixing in the occasional changeup (5% of pitches in 2015). He does throw two varieties of fastball, four seam and sinker, with about 45% of his pitches overall being sinkers in 2015, and a further 20% being fourseam fastballs according to Brooks Baseball.

Both of Nova's fastballs sit at 93-94 mph, while his curve (30% of pitches thrown in 2015) features sharp 12-6 downward movement that generates an above average rate of swings and misses. When Nova attacks the zone, his toolkit as a pitcher allows him to both generate whiffs and groundballs, which is a highly desirable combination for a reliever coming out of the bullpen with runners on base.

Sabathia also features two fastballs, a four seam (28% of pitches overall in 2015) and a sinker (30%), as well as a changeup (19%), and a slider (22%). In terms of his off-speed offerings, Sabathia utilizes both his changeup and slider when facing righties, but turns almost exclusively to his slider when opposing left-handed batters.

Against lefties, Sabathia throws a fastball (four seam or sinker) 53% of the time, and a slider 43%, while rarely mixing in a changeup (3% of his pitches against left-handed batters). So while at first glance it might appear that Sabathia's pitch repertoire is ill-suited to a bullpen role, particularly given his diminished stuff, his fastball-slider combination is amenable to a bullpen role where he is primarily used to match up against lefties.

Facing Same-Handed Batters

Both Nova and Sabathia performed far better last year against same-handed batters than against hitters facing them from the opposite side of the plate. Against righties, Nova yielded a .682 OPS, five home runs, and 15 walks against 204 total batters faced according to FanGraphs in 2015. In stark contrast, against 209 left-handed batters, he yielded an .899 OPS, eight home runs, and 18 walks.

Sabathia's splits are similarly dramatic. Against 589 right-handed batters he gave up 25 home runs, 45 walks, and allowed an opponents' OPS of .862. Against 137 lefties, Sabathia yielded three home runs, five walks, and an OPS of just .518. Particularly striking is the number of left-handed batters that Sabathia faced in 2015, 137 in 167 innings of work. Opposing managers stacked their lineups with right-handed batters against Sabathia last season, and with good reason, as he dominated lefties and struggled mightily against right-handed batters.

With Runners On Base

Neither Nova nor Sabathia pitched particularly well with runners on base in 2015. Nova surrendered an .850 OPS with runners on, while Sabathia was only slightly better with an OPS of .833. Their struggles were similar pitching from the stretch, as both allowed an inordinately high number of walks (16 in 44.2 innings for Nova and 25 in 73 innings for Sabathia) and home runs (nine for Nova and 11 for Sabathia) when they got into trouble. Both Nova and Sabathia pitched worse from the stretch than they did from the windup in 2015, making each of them dubious candidates for the bullpen in 2016.

With results along these three dimensions in mind, two points jump out regarding the decision that the Yankees face in choosing whether to send Nova or Sabathia to the bullpen. First, neither is a natural fit for the bullpen given their struggles pitching out of the stretch, and in particular their propensity to give up walks and home runs with runners on base.

Second, the most translatable skill that either possesses for a move to the bullpen is Sabathia's ability to get left-handed batters out. Sabathia was mediocre at best overall in 2015, but he pitched great against lefties and clearly still has the necessary tools to make left-handed at-bats against him quite difficult. The problem for Sabathia at this stage in his career is that the vast majority of hitters that he faces are righties, making it tough for him to be successful.

Pitching Sabathia out of the bullpen would offer Joe Girardi the best opportunity to exploit his talent for getting left-handed batters out, and also limit his exposure against righties. Nova matches up better against righties than lefties, but his splits are less stark than those of Sabathia.

It is very likely that at some point during the season injuries will make this debate moot, and force both Nova and Sabathia into the starting rotation. For the time being the Yankees have a choice to make, and if optimizing the overall performance of their pitching staff is their goal, Sabathia will move to the bullpen where Girardi will be positioned to utilize his ongoing ability to dominate left-handed hitting.