How homer-prone is Nola, really?
For all official purposes, baseball begins on opening day. For all personal purposes, though, baseball begins once some small, individual ritual has been fulfilled. It may be the first bite of the season’s first hot dog. It may be the first time you put on that old favorite jersey. For me, it’s the first time I fill out the lineups in my scorebook.
For a lot of Phillies fans it seems that the season hasn’t truly begun until there’s an Aaron Nola-surrendered homer to complain about. Thus, for a certain percentage of the Phaithful, the 2025 season officially got underway on Sunday, when Nola allowed Josh Bell to send a 3-run blast just over the wall at Nationals Park’s center field. This produced the familiar pattern across the city and her surrounding environs: the wince as the ball left the bat with a mighty, resounding clap, the wince becoming a grimace as the ball left the yard, the grimace ceding way to a groan of exasperation. For all the good Nola has done for the Phillies in recent years (and it should not be forgotten that whether we assess his pitching by quantity or quality he has contributed enormously to the cause shared by all those who wear red pinstripes), he has, like American Airlines after they made the questionable decision to sell lifetime passes, seemed to be a frequent victim of the round-tripper. What a player seems to do, however, isn’t enough to tell us what they really do. What do the underlying numbers say about Nola and the long-ball?
Aaron Nola led all Phillies pitchers in bombs surrendered in 2024 with 30, 6 more than the next closest Phillie hurler (Taijuan Walker). He led in the same category in 2023 with 32, (Zack Wheeler was in 2nd place with 20), finished 2nd in 2022 with 19 (Kyle Gibson allowed 24), 1st in 2021 with 19, and 2nd in 2019 with 27 (1 behind Zach Eflin). And his numbers in this regard are worrying in comparison to the rest of the league, too: he finished 5th overall in deliveries-turned-dingers in 2024, 6th in 2023. The complaints are thus not without merit: Nola really does allow a lot of homers, whether we compare him to his fellow Phillies or to his compatriots league-wide.
But total homers allowed, while certainly the most relevant statistic when it comes to our emotional state as Phillies fans, isn’t necessarily the best one for evaluating Nola’s tendencies. In addition to giving up a lot of four-baggers, Nola also throws a whole lot of innings. It stands to reason that the more innings a pitcher throws, the more gopher balls they’ll accrue. So we ought to look at HR/9— the number of downtowners allowed per 9 innings pitched instead. Nola allowed a HR/9 of 1.35 in 2024, 9th highest among Phillies pitchers with at least 10 innings pitched, and 2nd highest among Phillies starters. His figure was 1.49 in 2023, placing him 4th from the top. The average HR/9 in those seasons, league-wide, was 1.1 and 1.2, respectively. So the numbers leave no doubt: Nola really does allow more taters than average Joe Throws.
I’ve been watching a lot of House, M.D., lately. Or rather, I’ve been watching a lot of clips of House, M.D., thanks to YouTube’s algorithm. I could blame the engineers over at Google who’ve developed remarkably effective ways at capturing attention; I choose instead to blame Hugh Laurie for being entirely too captivating in his role (and not just that role, go watch Jeeves and Wooster if you haven’t seen it). That aside, I’ve been in the mood to play faux-diagnostician lately. The first thing you ought to do in the diagnostic process is rule out the simple, more explanations before seeking out a deeper problem. Could it be the ballpark?
There’s no place like home, but that uniqueness is not always positive. The dimensions of Citizens Bank Park, resembling those of the charmingly intimate “bandboxes” of the past, have not been entirely friendly to the man who is presently her longest-tenured resident. By park effects, Citizens Bank Park was the 6th-most homer friendly park in 2024 and the 7th-most in 2023. If every game Nola pitched in 2024 had been in CBP, he would’ve surrendered 38 homers rather than the 30 he really did. Only Cincinnati’s Great American Ballpark, the league’s most homer-happy stadium, would’ve been worse for him (39 xHR). In contrast, if every Nola start that year had been transplanted to Detroit’s Comerica Park, he would’ve allowed only 19 homers. That’s not a one-year fluke either. In 2023, again only Cincinnati would’ve been a worse home for Nola in regards to homers (though Dodger Stadium and Atlanta’s Truist Park would’ve been as rough as CBP). But while this does contribute to Nola’s tendency to give up the longball, it can’t explain all of it. After all, Nola gives up more homers than many of the other Phillies pitchers, all of whom play their home games at the same home.
Maybe luck has something to do with it? Baseball Savant calculates expected HR allowed, which assesses whether the homers surrendered would’ve been homers at parks other than the ones in which they were hit. It turns out Nola has been a bit unlucky: using adjusted xHR, which accounts for wall height, wall distance, and environmental impacts, Nola allowed 6 more homers than expected in 2024 and 5 more in 2023. Still, even if he had only allowed the number of moonshots that the metrics suggested he would in 2023 or 2024, he still would’ve led or tied all Phillies in homers allowed. So bad luck has made him look more homer-prone than he really is recently, but there really is an underlying problem.
Or at least there has been over the past 2 seasons. In 2022, he had a career-best HR/9 of 0.83, well below the league average. He also posted sub-1 HR/9s each year from 2016 to 2018. So we’ve got a pair of questions to answer: why has Nola allowed so many rainbow drops over the past 2 seasons? And what happened in 2022, when he was better than average at avoiding them?
We’ll take a look at that in part 2.