Analyzing Fly Ball Metrics: 2020 Positive Regression Candidates

A once intermittent and revered event, the home run ball has now engulfed baseball to extraordinary levels, which has theorists convinced that the ball is tampered with or "juiced." For a good reason, as last year we saw four teams shatter the single-season home run record previously held by the 2018 Yankees, with the Minnesota Twins surpassing the mark with a full month of baseball still left on the calendar. 10 teams from the 2019 season now sit in the top-20 on the all-time list, while 15 clubs established new franchise bests for home runs in a season. While it's true that home runs have seen a gradual rise over the last decade, it certainly raises an eyebrow to see such a universal boom across the entire league.

This dramatic spike in souvenirs meant that a lot of pitchers became casualties during this outbreak. Whether a juiced ball was a direct impact or not, we'll try to uncover which hurlers are primed for some positive regression in this area for the 2020 season. A few stats that are imperative to this topic include Home Runs per nine innings (HR/9), Home Run to Fly Ball Rate (HR/FB), as well as Statcast metrics such as fly-ball rate (FB%), Barrel%, and Exit Velocity (EV). These measures are often normalized over an arbitrary period of time, so when numbers appear inflated at season's end, we can predict who will likely regress back to the mean the following season.

Baseball is a game of averages, and it can take years for a player to develop enough of a sample size to find an accurate representation of their underlying metrics. Now that we have our heads wrapped around what we're looking for in our candidates, let's start breaking down some data.

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Chris Sale (SP, BOS, 37.3 ADP)

A lot of Chris Sale's failures from 2019 had to do with his inability to keep the ball in the park. He entered the year with a career 11.2% HR/FB and a 0.90 HR/9, but his results in 2019 exploded to a 19.5% HR/FB and 1.47 HR/9. If we look at a few Statcast metrics we see an overall decline, but nothing too egregious.

Sale's Barrel% and EV in 2019 were both career lows, but his fly-ball rate was nearly identical to his career mark. With his batted ball metrics dipping below his lifetime norms, it's no surprise he surrendered more round-trippers last season, but a near double-up in HR/FB seems inflated. There's not enough here to truly explain Sale's monumental increase in homers until we look at some fastball data.

Sale didn't start throwing a four-seamer until he joined the Red Sox in 2017, but his 93.4 MPH velocity last year was by far his slowest season with the heater. Down nearly two ticks from the year before, he had trouble with velocity out of the gate, averaging 92.4 MPH on the fastball in April. Five of the 12 homers he allowed on this pitch were in this month before regaining some speed, but his home run numbers still didn't completely level out the rest of the way. Hitters also attacked this pitch more aggressively, swatting 10 dingers on the first two pitches of an at-bat after he allowed just two in 2018.

Sale's diminishing velocity that stemmed from elbow problems was undoubtedly a contributing factor to his home run susceptibility last year. It wasn't like he was serving up no-doubters on a regular basis, however, as his 390' average home run distance placed him in the 95th percentile of the league last season. If the lefty can get his velocity back up in 2020 and become more deceptive early in the count, expect some positive regression for the upcoming season.

Blake Snell (SP, TB, 35.5 ADP)

Coming off a Cy Young season in 2018, Blake Snell struggled to retain his form with the Rays before an elbow issue in July caused the southpaw to miss nearly two months of action. His trophy defense started on a sour note right away as he gave up three long balls on Opening Day, which was a sign of things to come in his age 26-season.

The chart above illustrates that Snell was much better at limiting fly balls and opponent's barrels last season, yet was tagged for nearly a 50% increase in HR/9 on almost the same EV. Most of the blame attributes to his curveball, which yielded six big flies last season after allowing just one throughout his entire major-league career. His curve was still generating whiffs, but the break on this offering didn't have the same movement that it did in any of his previous years. Hitters took advantage of the lack of elusiveness by clubbing all six of them out before July.

Snell made an adjustment when he toed the rubber for his first start in July as his movement normalized over his next three outings. He landed on the IL after these starts but kept his curveball metrics in line when he returned for three appearances in September. Opponents never even put this knee-buckler in play during this combined six-game sample, which included 67 pitches worth of opportunity. With Snell's most elusive pitch working at top effectiveness, he should put his home run woes behind him and return to All-Star form in 2020.

Trevor Bauer (SP, CIN, 83.8 ADP)

Trevor Bauer had one of the more notable increases in HR/9 last season, but by looking at the chart below, it appeared he went from his floor to his ceiling in just one year.

His marks entering the 2019 campaign split his yearly numbers almost right down the center as the law of averages did its finest work. Bauer's fly-ball rate did uncharacteristically increase nearly 7% over his career mark in 2019, but the average EV on his fly balls and line drives saw only a small uptick from 92.1 MPH to 92.4 MPH.

Bauer's four-seamer can take most of the credit for his home run struggles since it surrendered 20 big flies a year ago after allowing 19 over his previous three seasons combined. His fly-ball rate on this pitch went up 4.6% from 2018 and became his most hittable offering as opponents barrelled it up a troublesome 12.6% of the time. It got worse for Bauer when he joined the Reds, giving up eight homers in his final five starts with six of them coming off the four-seamer.

Perhaps fatigue set in on the right-hander as his 93.6 MPH velocity on his fastball in September was by far his lowest of any month. His 213.0 innings pitched was nearly 38 innings more than the year previous, and it also marked the first time he eclipsed 190 IP in his career. The move to Great American Ballpark won't do Bauer any favors as it grades as one of the more hitter-friendly parks annually, but judging by his lifetime marks, it's hard to expect his 2019 home run pace to continue.

Shane Bieber (SP, CLE, 28.2 ADP)

Shane Bieber excelled in the minor leagues when it came to limiting the long ball. He posted a 0.39 HR/9 across 277.0 minor league innings, and when he got to the majors in 2018, he still managed to hold a respectable 1.02 mark. Things got much worse in 2019, however, as his HR/FB crept up 4% to 16.1% as he surrendered 31 dingers in 214.1 IP (1.30 HR/9).

Bieber's fly-ball rate went down 2% from his rookie campaign to what was still a below-average 21.7% mark. Unfortunately, his 93.1 MPH fastball was extremely hittable, as indicated by the chart below. His four-seam went from his best fly-ball pitch in 2018 to his worst last year as opponent's eyes lit up upon delivery. This decline led to 19 homers surrendered by the four-seamer, including five in the final month, when his velocity started to fade.

So what makes Bieber a positive regression candidate in 2020? First, he allowed 12 homers on the first two pitches of the at-bat with nine coming off the fastball. With more maturity and unpredictability, he can nip this in the bud, and he has the minor league track record of supporting regression. While his minor league home run numbers certainly won't translate directly, his average HR distance of 391' that placed him in the 93rd percentile suggests a possible juiced ball sent a few more balls into the bleachers than normal. Bieber is a perfect example of a player waiting for sample size to regulate his numbers, so anticipate a pullback closer to his 2018 home run metrics this season.

Matthew Boyd (SP, DET, 167.6 ADP)

Matthew Boyd has always struggled to keep the ball from reaching the bleachers, but in 2019 his 1.89 HR/9 sat as the worst mark among all qualified starters. After posting a 1.43 mark in 2018, the southpaw entered the season with a career 1.55 HR/9 and a 12.4% HR/FB. An 18.% HR/FB last season led to him allowing a whopping 38 long balls, 25 of which came off his four-seamer.

Boyd lowered his fly-ball rate on his fastball from 39.4% to 29.8%, yet the ball kept flying out of the stadium at a higher clip. He doesn't have an electrifying four-seamer, but he increased the speed on this pitch by over 1.5 MPH to 92.1 MPH and even gained velocity as the season progressed. Perhaps the 28-year-old's dependency to throw the fastball hurt him as he upped his four-seam usage by over 15%, essentially becoming a two-pitch pitcher. Boyd began incorporating his changeup more frequently in September, which was his best statistical month besides his torrid start in April.

Despite pitching in a middle-of-the-pack home ballpark in terms of Park Factor, Boyd surrendered 26 dingers at home (2.71 HR/9) after allowing eight (0.9 HR/9) at Comerica Park the year previous. Fittingly his HR/FB catapulted from 7.0% to 22.8% despite seeing a near 5% decrease in fly balls. Boyd's 74th percentile finish in FB/LD Exit Velocity (92.0 MPH) suggests he was the recipient of some unfortunate batted ball events, and it's difficult to see these numbers remain this elevated in 2020.

Miles Mikolas (SP, STL, 223.4 ADP)

Miles Mikolas couldn't find the same success from 2018 in his second season back in the majors with the St. Louis Cardinals. The long ball had a lot to do with it since his HR/9 went from 0.72 to 1.32, with nearly a 7% increase in HR/FB to 16.1%. Mikolas limited opposing right-handed bats to four round-trippers in 2018, but notably struggled against them last season as they tagged him for 16 HR. His fly-ball rate versus these hitters remained identical from season to season (26.2%), but yet his HR/FB sky-rocketed from 6.0% to 20.3%. A jump like this is bewildering, but some of the blame lies in his ineffectiveness with his slider, the pitch he predominantly uses against righties.

Mikolas' slider lost one full tick on the radar gun but kept its break to similar levels from 2018. He threw it in the zone less often than in 2018 and batters, in turn, swung at it fewer in 2019 but took advantage when he did hang one over the plate. Still, his 27.6% HR/FB allowed on the slide piece last season seems unsustainable at that high of a level.

Thankfully Mikolas' Barrel% against the pitch gradually fell as the season progressed since he began to paint the corners more and leave fewer balls over the plate. Overall, Mikolas dropped his HR/9 to 1.17 in the second half, and a number in that realm seems more likely to remain near his mean moving forward.

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