Where Is Kevin Gausman’s Fastball Going?

For the Braves, there is no rush to determine what Kevin Gausman is. With two more years to ponder that question and an NL East title right around the corner, any sense of urgency in Atlanta is directed toward the playoffs. Yet Gausman’s dominance since being acquired makes his future a presently compelling storyline.

A non-waiver deadline addition, Gausman owns a brilliant 2.61 ERA in 48.1 IP for Atlanta and a still quality 3.88 FIP and 93 cFIP. He has played a significant role in wrapping up the division race, and he should continue to be a pivotal piece in the playoffs and beyond, but the question remains of how high his ceiling actually is.

In Atlanta, Gausman has given up plenty of hard contact (44.2%) and seen his strikeouts dip further (16.1%), but on the promising end of things, his home run problem has succinctly if temporarily cleared up. While it is tough to glean much from 8 starts, given the Braves’ reputation for churning out reputable starting pitchers, it is always tempting to feel like they know something we don’t, and they might know a thing or two about Kevin Gausman.

Surely, they know his 4-seam fastball has declined in recent years per metrics from Baseball Savant and Brooks Baseball:

Year	Avg. Velocity (mph)	Spin Rate (rpm)	Avg. Vertical Movement (in.)
2015	96.0	2349	11.18
2016	95.4	2307	9.82
2017	94.9	2247	9.50
2018	93.6	2165	8.89

The drop in velocity is hardly news, but the spin rate of his 4-seamer has also slipped from roughly 100 rpm above average to now 100 rpm below average. With that, the vertical movement on it has crept down as well, and altogether these factors conspire against its swing-and-miss potential.

Year	Whiff/Swing% against 4-seam FB
2015	20.55%
2016	18.60%
2017	17.84%
2018	15.26%

As the fastball has declined, batters have been able to steadily decrease their Whiff/Swing% against it. And this has meant trouble for Gausman as he’s had little luck finding outs with his fastball when batters don’t swing through it. Notably, they carry a .308 average and .486 slugging percentage against it since 2017.

But even when he boasted a stronger fastball, home runs were still a problem. Home runs on his fastball were still a problem. Now, home runs just…aren’t a problem.

Since being traded, Gausman has allowed only 5 home runs or rather a 0.74 HR/9 compared to a 1.4 HR/9 from 2015 to his last day with Baltimore. Just how sustainable that is may depend on the Braves’ plan for him moving forward, as he, presumably with their guidance, immediately made some adjustments upon his arrival.

So far with the Braves, Gausman has continued to use his fastball under 60% of the time, but he has also eased off his slider and leaned more on his splitter according to Brooks Baseball.

Stint	IP	Fastball%	Slider%	Splitter%
2018 w/ BAL	124	58.70%	15.86%	24.29%
2018 w/ ATL	48.1	56.64%	10.84%	32.38%

Gausman already didn’t rely much on his slider, but perhaps, he didn’t even need it that much seeing as batters have hit .303 and slugged .505 against it since 2017 while hitting just .185 and slugging .319 against his splitter. Apparently, the Braves were cognizant of this and advised him to more heavily favor his better secondary offering.

While throwing your best stuff more often is a straightforward adjustment, there may be something extra being implemented here as Gausman’s command and/or approach may have upticked since he arrived in Atlanta too.

Here are heatmaps of Gausman’s fastball and splitter with the Orioles this year:

And here they are with the Braves:

Gausman has been able to keep his splitter from taking off laterally too often and thus has more consistently kept the pitch down and out of the zone. With his fastball better concentrated on the arm-side edge as well, he has established a different relationship between the two pitches. As a Brave, Gausman has achieved greater and mostly vertical separation between the two pitches on average, but as an Oriole, the average difference was tighter and more two-dimensional even though his splitter, like most, has similar horizontal movement compared to his fastball.

In the process of successfully making this adjustment, the splitter has become a consistently present piece of Gausman’s repertoire — RHBs are seeing more in all counts; LHBs are seeing more both ahead in the count and on the first pitch — and it has possibly even improved.

Batters have been able to elevate the splitter more often, but when they have elevated it, they haven’t driven it. Gausman has only allowed one extra-base hit on it — a double — since the trade. Batters’ average exit velocity on flyballs and line drives against it has dropped from 91.4 mph to 83.9 mph, and accordingly, his xwOBA on these balls has dropped from .640 to .419.

To some extent, that success probably won’t keep up. That 83.9 mph exit velocity is the lowest in the league since August among pitchers with at least 5 batted ball results under these specific conditions and it is well below league average (91.5 mph). That’s not to say Gausman couldn’t chuck the toughest splitter in the league though. That has been near reality for a while but could be truer now than ever.

Yet taking that next step — the one everyone in Baltimore waited on for years — might hinge on what Gausman can do with a seemingly improved fastball.

Stint	GB/BIP	LD/BIP	FB/BIP	PU/BIP	wOBA	BABIP
2018 w/ BAL	42.37%	27.12%	25.00%	5.51%	.399	.364
2018 w/ ATL	47.00%	27.00%	26.00%	0.00%	.314	.263

Gausman’s fastball has been coaxing a few more groundballs as you might expect from a (relatively) low-spin 4-seamer, but that improvement has evidently borrowed from its pop-up rate and its flyball rate has remained steady. Partly because of this, his fastballs have a still uninspiring .419 xwOBA with the Braves compared to .394 with the Orioles. Also taking into account its low BABIP, there could be some fairly steep regression baked in here.

Ultimately, Gausman’s home run troubles may yet persist unless he can also temper his fastball’s flyball rate. He could already have one foot in the door with his fastball developing groundball-inducing qualities and his groundball rate trending upward in general, but you won’t mistake him for a flyball-contact manager (no matter how hard Ender Inciarte tries to fool you). He’ll still have to mitigate damage elsewhere and not count on his 8.7% HR/FB to remain so low. The splitter will help, yet to truly move the needle, it will need to play up off a fastball that has been declining for years.

All stats referenced prior to games on 09/15/18