Some Like It Hot. What about Nola?

Does the pitcher from the Pelican State struggle in the cold?

“Some guys are just like that.” So said Rob Thomson about Aaron Nola this past Saturday. There are a number of ways in which Nola is “just like that”— some guys just have excellent hair, some guys are just particularly likely to pitch a large number of innings, etc. But in this case, Thomson was referring to Nola’s apparent struggles in colder weather. After a second consecutive rough start, this one against the Dodgers to the tune of 2 homers, 7 hits, 3 earned runs and just 2 strikeouts, Thomson suggested that Nola’s early season struggles (his first start, a 2-homer loss to the Nationals, wasn’t great either) were the result of the time of year, with his performance, and particularly his fastball, likely to take a leap as the weather got warmer.

This is not the only narrative that has emerged around the long-haired hurler’s powers waxing and waning in relation to the month. There was a long-standing narrative of Nola being replaced by the lackluster September Nola in the fall (and perhaps there still is; we’ll see if the talk heats up as we approach the final months of the season). Putting aside late-season Nola for now, there is good reason to take Thomson’s idea seriously. For one thing Thomson knows Nola and his tendencies quite well (as do the baseball operations staff that may be informing his thoughts on the matter). If he thinks Nola’s performance is largely the result of the temperature, that’s worth taking seriously.

There’s ample evidence to demonstrate that offense increases as the weather warms up (warmer air makes the ball travel farther), so it may seem counterintuitive that a pitcher would do worse in colder weather. But there is demonstrable proof that pitchers typically take some time to reach their full effectiveness, and that there is a particularly large increase in velocity between April and May. It stands to reason that some pitchers will take longer than others to ramp up to their ceiling, and that some pitchers will struggle more than others in the early going as a result. The logic behind Nola’s early struggles being the result of the month, whether that be because of discomfort in lower temperatures or simply a need for more time to work up to his peak, is reasonable. But first things first: has he really struggled in the earlier parts of the season?

Here’s Nola’s ERA by month since 2021:

(If the years aren’t showing up on mobile, his April 2021 ERA is listed first, then April 2022, and so on).

There doesn’t seem to be much of a clear indication of a temperature-based trend here (though there is plenty of evidence for the September Nola thing). Nola’s ERA increased from April to May in 3 of the last 4 seasons, and his June ERA was higher than his April ERA in 3 of the last 4 as well.

Here’s his WHIP by month:

There’s not much of a clear narrative here, either. In all of the past 4 seasons, Nola’s May WHIP has been equal to or higher than his April WHIP. In 3 of the past 4 seasons, his June WHIP has been higher than his April WHIP.

So there’s little to suggest Nola’s performance suffers in the cooler temperatures of April, at least not in the big-picture numbers. But Thomson drew particular attention to Nola’s fastball, suggesting that Nola requires greater time to get that pitch to its peak. That may be where the answer lies.

And so here’s a whopper of a chart that we’ll call “Everything You Wanted To Know (And If We’re Being Honest, Probably Much More) About Nola’s 4-Seamer Performance By Month”. This is across his whole career (so all May results combined, etc.)

Nola’s fastball velocity is indeed at its lowest in March/April, sitting about 1 MPH below his peak speed. His 4-seamer spins a little less in the cooler months too, which would limit its carry. Both of these factors might make it easier to hit.

But Nola’s 4-seamer doesn’t have an unusually high BA allowed in March/April. His BA allowed against the heater jumps from Mar/April to May, declines through July, then spikes again in August and September. Similar patterns are observed for the OBP and wOBA against the fastball. There’s no real indication there of a temperature-based change or a time-based one with any of those statistics.

But there may be one with slugging percentage. Nola’s slugging percentage allowed with the heater is .422 in March/April; the only month (or combination, rather) with a higher one is September/October. Perhaps this suggests that Nola isn’t more likely to give up hits with the fastball in March/April, but that the hits that he does allow with it in those colder months are more likely to be big ones (that would go against the general trend of balls flying further in warmer months, but that could be offset by the effects of a slow-ramp up).

But this is starting to feel a bit like cherry picking. Nola’s fastball is measurably slower in the early months of the season then it is at mid-campaign, so there is something here. But it’s hard to see the impact of this, if any, on his overall performance. It’s possible that there is no real narrative behind Nola’s subpar duo of starts at the dawn of the 2025 campaign, that it’s variance, luck, a bad break or two. That may be less satisfying than a narrative that explains away the performance, and that promises better ones will come with higher temperatures as sure as May flowers follow April showers. The less satisfying answer, however, is sometimes closer to the truth. Nola is an excellent pitcher, but he’ll put up a bad start or two every now and then.

Well, nobody’s perfect.