Corbin Burnes must diversify his approach against left-handed hitters

The Brewers have not lived up to expectations this season. While they still have time to make a push for their fourth consecutive postseason appearance in four full seasons, the clock is ticking. Milwaukee remains on the outside looking in with two weeks of regular-season play remaining.

The root of the club’s shortcomings is obvious. The Brewers allow too many runs for a team built upon run prevention. Last season, their pitching staff ranked third in baseball with an 83 ERA-. This season, they are tenth with a 98 ERA-.

Injuries have ravished the starting rotation and left the staff limping toward the end of September. Aaron Ashby returned on Tuesday night from a month-long stint on the injured list and is not fully stretched out. Eric Lauer and Freddy Peralta are nursing balky elbows and shoulders.

Making matters worse is that Corbin Burnes has battled an uncharacteristic bout of struggles since the start of August.

The right-hander was authoring a strong follow-up to his Cy Young Award-winning campaign, posting a 2.31 ERA and 2.92 FIP through the end of June. In his last 10 starts, he has scuffled to the tune of a 4.80 ERA and 4.11 FIP.

While his season-long numbers—a 3.12 ERA and 3.30 FIP—remain strong, Milwaukee’s ace has failed to step up when the team has needed him most. During this stretch, he has thrice allowed at least five runs in a start, including his latest clunker against the Mets on Monday night.

It’s unfair to shoulder the majority of the blame for the staff’s struggles on Burnes, and it’s worth acknowledging his 14-strikeout gem against the Giants and his gutsy outing against the Cardinals earlier this month. However, the Brewers may not be able to afford any more underwhelming outings from their best arm.

Burnes has continued to dominate right-handed opponents. Since the start of August, he has held them to a mostly harmless .269 wOBA, making this one of his best stretches of the season against right-handers.

On the flip side, left-handed hitters have tagged Burnes for a .345 wOBA during this underwhelming run of starts. The past two months have represented the most damage lefties have done against him since 2019.

While he mixes in sliders and sinkers against right-handers, Burnes effectively becomes a three-pitch pitcher against lefties. He throws his cutter a whopping 62.1% of the time in these matchups and supplements it with his curveball and changeup.

While his curveball has continued to stifle opposite-handed opponents, Burnes’ cutter and changeup combination is now hurting him after being untouchable just a couple of months ago.

The back-door cutter is the backbone of Burnes’ approach against lefties. He typically tries to paint his cutter on the outside corner and pairs it with a changeup that starts in the same tunnel before fading off the plate.

This sequence has enabled Burnes to put away lefties easily, but hitters have started to flip the script by focusing on the outside part of the plate.

The new approach is reflected in Burnes’ splits on back-door cutters to lefties. For this analysis, the sample includes pitches in the strike zone and those just off the plate (pictured below), so it covers most of the pitches Burnes attempted to land on the outside corner.

Lefties are jumping on the back-door cutter after doing virtually nothing with it for much of the year. Here are a few examples, starting with former Brewers farmhand Cooper Hummel blasting an outer-third cutter to the wall after Burnes left it elevated.

Here’s another one that was left up and shot into the gap by Mike Yastrzemski.

This cutter to Alec Burleson was in a better location, but he was ready for it and slashed a 100 mph line drive to left field.

Finally, here’s a perfectly-executed back-door cutter that Daniel Vogelbach rocketed into the gap on Monday night.

Lefties have recorded 13 hits against Burnes’ cutter in September, the highest total of any month this season.

Burnes’ spotless opponent wOBA on back-door cutters in August is deceiving. While lefties did not record a single hit when he successfully executed the pitch, they notched 11 hits against the cutter overall.

Most of those hits occurred when Burnes attempted to paint the cutter on the outside corner but missed down the middle. (For what it’s worth, three of the four hits against inside cutters were courtesy of the Dodgers, who boast what is arguably baseball’s best lineup.)

Burnes has also allowed more damage to lefties against his changeup during this rough patch. After they did not manage any extra-base hits against it through the end of July, they have since hit three home runs.

Location appears to be the main culprit. Two of the changeups in question were above the belt, and the third came on a two-strike pitch that was not supposed to catch the zone.

Interestingly, Burnes has ramped up his changeup usage against lefties as the season has gone on after previously using the curveball as his go-to secondary pitch.

Meanwhile, the spin rate on his changeup began to spike. It has now added over 250 rpm since May.

A changeup that spins more tends to fade less as it approaches the plate because the spin counteracts gravity’s pull on the ball.

Burnes is now sitting well above the league-average changeup spin rate of about 1700 rpm, so the added spin may have made his changeup less deceptive. However, Statcast has recorded no changes to the shape of the pitch, and its whiff rate has increased. Perhaps the split came down to nothing more than a handful of poorly-location pitches.

Hammering the outside corner with cutters and changeups has been Burnes’ game plan against lefties for the past three seasons. It appears those hitters are starting to adjust to that approach and are specifically hunting the cutter on the black. Now it’s on Burnes to counter.

The most effective adjustment may be to start front-dooring some sinkers on the inside corner of the plate to keep hitters off the outer third. He could also consider throwing more curveballs or more cutters up and in.

The Brewers need their ace to step up over the final weeks of the regular season. To do that, he may need to start giving left-handed hitters more areas of the zone to cover.