Flu-Like Symptoms: The Coming Popup Plague

Sometimes, when you set out to find out something, you discover something else that’s more interesting. This is one of those cases. Let me walk you through it.

Last week, I noted that the Padres’ ratio of very boring plate outcomes—strikeouts and popups—compared to exciting plate outcomes—total bases—is running at an all-time high. That got me thinking. We all know that strikeouts are going to set yet another record this year. What about popups?

You might think that with batters seeking to hit balls in the air more, we’d be seeing more popups. Well, you’d be wrong. Here are popups as a percentage of all batted balls since 1989.

Big caveat here: The sources for batted-ball data have switched around over the years, so the definition of a popup has shifted a bit too. (You can tell that by looking at the graph.) But it’s still clear that we’re not headed for a record in 2017.

But, of course, as we know, fly balls aren’t really up that much. There have been, to date, more ground balls hit as a percentage of all batted balls (45.5 percent) than were as recently as 2009 (45.0 percent). So if batters aren’t hitting a lot more balls in the air, we shouldn’t be expecting a spike in popups. The right way to look at popup frequency is as a percentage of all air balls (fly balls, line drives, and popups):

Still, we’re not anywhere near a record pace. So there’s at least one aspect of baseball in 2017 that doesn’t warrant complaints! Popups are not reaching epidemic proportions like strikeouts and home runs and Three True Outcomes and game lengths and time between pitches and mound visits and …

And that’s borne out by looking at team totals as well. Since 1989, here are the teams that hit the highest proportion of popups as a percentage of air balls:

Consistent with the graph above this table, the golden age for popups since 1989 was in the last century, not this one. The highest-ranked team since 2000 is the 2004 White Sox, who popped up 19.1 percent of their air balls, the 16th-highest total. Only 10 of the 50 teams with the highest popup-to-air ball ratio are from the 2st century.

And then along came this year’s Padres.

No, they’re not going to crack the top 10. They might not even crack the top 50. But in an era of decreased popups, they are the outliers, the leaders of the pack (all 2017 data in this report through games of July 22):

No other team is popping up as many as 16 percent of their air balls. The Padres are pushing 18 percent. They’re on a pace to have the 78th-highest ratio since 1989. The next closest team, the Red Sox, are on pace to finish 294th.The Padres’ popup rate is in the 91st percentile. Boston’s is in the 65th.

Why are the Padres popping up so much? Well, for starters, they really aren’t very good. That explains a lot! They are:

• Last in the league in runs (362), batting average (.235), on-base percentage (.301) and strikeout rate (25.6 percent)
• Second-to-last in OPS (.698), VORP (98.2), and average exit velocity (85.0 mph)
• Third-to-last in slugging percentage (.398) and TAv (.256)

As for individual players, here are all Padres with 70 or more plate appearances.

And here’s where the research took me in an unexpected direction. Note those averages at the bottom. The Padres as a team are hitting an only slightly above average 53.8 percent of batted balls in the air, but their 17.4 percent popup-to-air ball ratio is way above the league average. Looking at individual players, you’ll see that the three Padres with the highest percentage of air balls—Schimpf, Szczur, and Hedges—all have popup-to-air ball ratios in excess of 24 percent, which is really high. Is that a trend? Do the most extreme air-ball hitters generate the most extreme popup ratios?

To check it out, I took every batter in the majors with 68 or more plate appearances this year and ranked them all in descending order of air-ball percentages, from the aforementioned Ryan Schimpf at 79 percent to Daniel Robertson at 28 percent. This gave me 410 players. Then I divided them into 10 groups of 41 players each. For each group, I calculated the average air-ball percentage and the average percentage of popups per air ball for all the players in the group’s batted balls.

Look, I know, this isn’t a sophisticated analysis. I’m using only players with a threshold number of plate appearances (which introduces selection bias), I’m divvying up my groups by number of players rather than batted balls (creating unequal decile sizes), and I’m guilty of the sin of binning.

But the overall trend is compelling. If you hit more balls in the air, you’re going to get more popups. That’s a given. And this seems to suggest further that if you hit more balls in the air, a greater proportion of those balls are going to be popups. Here’s a graphical representation.

Actually, a scatterplot is more compelling in this case. Here it is:

If you prefer numbers to pictures, the correlation coefficient between the average air-ball percentage per decile and the average popup/air-ball ratio is 0.88. As air balls rise, so does the percentage of air balls that are popups.

So, yeah, we’re not heading toward an all-time high in popups, which would be boring. That’s good. But if the so-called air-ball revolution continues, and fewer balls are hit on the ground, we’re likely to see not only a commensurate increase in popups, but also an increase in the proportion of air balls that are popups. Think the Three True Outcomes are boring? Get ready for a rise in another boring outcome. If air balls continue to grow, popups look likely to grow faster.

Thanks to Rob McQuown for research assistance.