Red Sox starter Nathan Eovaldi is allowing home runs at an alarming rate

The long ball has plagued Red Sox starter Nathan Eovaldi this season

Nathan Eovaldi had a breakout season in 2021 to establish himself as the ace of the Boston Red Sox rotation. In many ways, he’s following up his career year with an even better season, with one notable exception. Eovaldi is coughing up home runs at an alarming rate.

Nasty Nate was brilliant against a loaded Toronto Blue Jays lineup on Monday, requiring only 72 pitches to cruise through seven innings. He struck out five without allowing a walk and gave up only two earned runs. That’s the type of line we’ve come to expect from Eovaldi.

Unfortunately, both runs scored on solo homers by Lourdes Gurriel Jr. and Matt Chapman. The home run by Chapman, which came with two outs in the seventh inning, was a rocket to left center field that traveled 422 feet with an exit velocity of 107.2 mph.

Eovaldi has now allowed a major league-leading seven home runs through four starts, an uncharacteristic trend for a pitcher who allowed only 15 in 32 starts last year. He didn’t allow his seventh home run until July 31 last season but he’s already reached that total before escaping April.

Strikeout rate and walk rate are two categories that Eovaldi was among the elite in last year and he’s currently on pace for the best marks of his career with a 10.0 K/9 and 1.2 BB/9. His 3.32 ERA would also be a career-best. The case for Eovaldi’s Cy Young award candidacy was built primarily on a 2.79 FIP that was the best among qualified American League starters last season. His excellent strike-to-walk ratio was a significant factor in producing a low FIP, as was his elite home run rate.

The switch has flipped this year. Eovaldi’s 0.74 HR/9 was the fourth-best among qualified major league starters last season but his 2.91 HR/9 is currently the second-highest. Despite improving his strikeout-to-walk ratio, the surge in home runs inflated his FIP to 5.60, well above his more appealing ERA.

How is it that in a season where power numbers are on the decline across the league, Eovaldi has suddenly become prone to surrendering home runs?

A review of his Statcast data shows some concerning trends. Eovaldi ranks in the 16th percentile with a 49.2% Hard Hit rate, the 15th percentile with a 91.7 mph average exit velocity and the 9th percentile with a 14.8% Barrel rate, per Baseball Savant. Each of those metrics would easily be the worst of his career.

Eovaldi hasn’t had a notable dip in velocity and his low walk rate proves his command hasn’t abandoned him. His issues appear to stem from locating certain pitches inside the zone. Working with a five-pitch arsenal allows Eovaldi to keep opposing hitters off balance but some pitches aren’t working for him so far this season.

The curveball is the only pitch in his repertoire that Eovaldi hasn’t allowed a home run on this season, which is no surprise considering only one of his home runs last year was hit against his curve. He’s dominated with the pitch, holding hitters to a .056 average.

The four-seam fastball is his most frequently utilized pitch. Five of his 15 home runs last year were against this fastball but only one of his homers this season has been against the four-seamer. His heater that averages nearly 97 mph isn’t the problem.

The cut fastball was his least utilized pitch last year at only 12.5% but that pitch was responsible for the most home runs with six. That trend has continued this year with two of his seven coming against the cutter despite throwing it only 8.7% of the time. It’s certainly not his best pitch but it doesn’t explain the drastic rise in home runs since he doesn’t throw the cutter very often.

Only one of his home runs has been against the split finger fastball but that already matches last year’s total with the pitch. The splitter has been far less effective this season despite being responsible for only one of his homers. Hitters are clobbering Eovaldi’s splitter for a .429 average and .643 slugging percentage, compared to a .183 AVG and .303 SLG against the pitch last year.

The main culprit has been his slider. Eovaldi has already allowed three home runs with his slider after giving up only two last season. The batting average against his slider is up from .269 to .308 while the SLG jumped from .433 to 1.000. His slider was one of his best weapons for putting away hitters with a 22.6 PutAway% last year but that has fallen to only 7.1% this season. Eovaldi’s whiff rate with the slider dropped from 35.1% to 26.1%.

Some of these metrics are small sample noise that will inevitably regress towards last year’s production over the course of the season. We can safely say that Eovaldi won’t surrender 50+ home runs so his bloated HR/9 rate is bound to fall dramatically.

What the data does tell us is that a couple of pitches that Eovaldi had success with last year have been ineffective to begin the season. Perhaps the rushed training camp didn’t give him sufficient time to harness all five of his pitches. His arsenal is deep enough that he can temporarily stay away from a pitch that isn’t working for him but Eovaldi needs to regain his previous form with the slider or splitter to return to the top of the rotation level he established last season.