How has J.A. Happ been so good for the Yankees?

The Yankees’ second half hasn’t been great, but that’s not to say that there haven’t been any bright spots. Perhaps the brightest among them has been the emergence of J.A. Happ as one of the Yankees’ most effective and reliable starters.

Since coming over to the Yankees at the trade deadline, Happ owns a 2.70 ERA across eight starts and 46.2 innings. He’s pitched six quality starts over that time, and his only real clunker has been his August 30 start against the Detroit Tigers. Happ has delivered nearly every time the Yankees have handed him the ball. He’s been the anchor for a struggling team.

Can Happ keep this up? Is his recent performance backed up a tangible change in approach, or is it just a hot streak aided by luck? The numbers provide evidence for both sides of the argument.

Happ is a good pitcher, but a closer look at his peripherals reveals that his results have been far better than his process. While his ERA with the Yankees has been 2.70, that figure is accompanied by a more pedestrian 4.44 FIP.

The main factors driving this ERA-FIP difference are his 93.1 LOB% and his .244 BABIP, both trusty indicators of a pitcher’s luck. Sure, some crafty hurlers like CC Sabathia have mastered the art of soft contact, demonstrating that their suppressed BABIP’s are a product of skill. However, that doesn’t seem to be the case with Happ, as his hard hit rate is up from 30.5% with the Blue Jays to 35.1% with the Yankees. Likewise, it’s safe to say that more luck is involved than skill with his sky-high LOB%, as his K/9, which correlates well with K/9, is down from 10.26 with Toronto to 8.29 in New York. Overall, Happ’s peripherals suggest that he’s had some luck with the Yankees.

That said, Happ’s pitch usage suggests that he’s changed his approach. More specifically, Happ has cut down drastically on his sinker usage, which was previously his bread and butter. According to Brooks Baseball, Happ has thrown fewer than 10 sinkers in each of his last five starts, the longest such streak he’s had since 2015, when he was having perhaps the best stretch of his career (1.85 ERA/2.19 FIP in 63.1 IP) whilst pitching for the Pittsburgh Pirates. Coincidence? Maybe not.

As a general trend, sinkers are falling out of favor with pitchers. Matthew Trueblood of Baseball Prospectus has theorized that it might be due to how the pitch interacts with other pitches in a hurler’s repertoire. Sinkers are similar to changeups in terms of movement, in that they both tend to have arm-side run and sink. This means that when sequencing pitches, throwing sinkers is not an effective way to set up changeups, as it becomes easier for hitters to pick up on changeups due to their similarity in movement.

This is true in Happ’s case as well, as his sinker is similar in vertical and horizontal movement to his changeup. A better pitch to set up his changeup would be his four-seam fastball, which, at an average velocity of around 92-93 MPH, creates more difference in velocity and in movement with his mid-to-high 80s changeup compared to his 90-91 mph sinker.

Sure enough, Happ has upped his four-seamer usage since coming to the Yankees, throwing it more than 70 percent of the time in September. It’s not clear how this has influenced Happ’s pitching, as aside from a much lower post-trade BB/9 (2.76 to 1.74) his peripherals haven’t turned for the better. The, the change is in itself drastic enough to warrant attention.

So, the stats are inconclusive as to the cause of Happ’s recent run. His peripherals say that he’s getting lucky, and that his skills are more indicative of a reliable mid-rotation starter than an ace. His pitch usage, however, suggests that Happ has changed his game up since coming over to the Yankees, although it’s not clear how that has affected his results. As the postseason approaches, the Yankees need as much pitching as they can get. For fans keen on finding out if Happ is really up to the task, his sinker usage, or lack thereof, is a trend to monitor in the final days of the season.