Starters have the highest RA9 for an April in years

Is it just the home runs? Is it a sample size thing? Or is something more going on?

Earlier this week, I wrote about how some of last year’s best pitchers have been off to a poor start this year. Watching baseball for the past month, it seemed to me that starting pitchers have struggled more than they have in the past, at least if we are comparing Aprils. I decided to take a look, and this is what I found. It needs to be mentioned that late March gets lumped in with April for the purpose of monthly splits.

I separated starters and relievers to see if there was anything there, but there was not much to conclude, though I was glad to see that I was not crazy to think that starting pitchers were allowing more runs. That number is up significantly compared to recent years.

Now you might be thinking that it is the result of the juiced balls. Well it has definitely been a factor.

Because so few plate appearances result in a home run, even small changes to HR% are meaningful. Still, it was not much higher than it was in April 2017 when starters had their lowest RA9 for an April in the past five years. The home run spike has hurt relievers much more, as they have a 3.3 HR% in April compared to a 2.5 HR% last April. However, starting pitchers are getting hit harder in general than they have compared to past Aprils.

Starting pitchers are getting more strikeouts than ever before, but they are also getting hit harder than they previously have when they are giving up contact. Hard-hit rate is calculated partially on the hang time of the ball, so it is hard to say how much of that is the ball and how much is the hitters just hitting the ball harder. For what it’s worth, the average exit velocity this season is 88.3 mph compared to 87.7 mph last year, as mentioned by The Athletic’s Eno Sarris.

While quite a few league stats become predictive early in the season as a result of so many plate appearances accumulating quickly, RA9 is not one of those stats, and that would be true even if we were looking at all pitchers and not just the starters. For example, starters had a 4.37 RA9 in April 2017, but finished at a 4.85 RA9 for the season.

So it is entirely possible that this early season trend is nothing more than a sample size thing. Beyond that, it is hard to find causes beyond home runs. I thought about whether pitchers are struggling with their command more, which is not unreasonable given the colder weather, because although we have a direct measure of control via walk rates, there is currently no way to measure how well a pitcher locates pitches within the strike zone. Even if such a metric were available, it would be hard to explain a collective loss in command beyond the weather, and obviously it is cold in much of the country every April. Regardless, I will certainly be interested to revisit this at the end of the season to see if this trend continues.