The other day, I was reading something written by Tom Verducci over at Sports Illustrated. Verducci was ultimately making an argument about Jacob deGrom and his Cy Young candidacy, but on the way there, he talked about what’s apparently been dubbed the Mystery of Flushing. The mystery concerns why the Mets can’t hit at home. More specifically, it’s about why the Mets’ team BABIP consistently suffers at home. Citi Field has been modified multiple times, but it was modified most dramatically before the 2012 regular season. Since 2012, the Mets rank last in the majors in runs scored at home. They rank seventh in runs scored on the road. And, since 2012, the Mets rank last in the majors in BABIP at home. They rank third in BABIP on the road. There’s an existing BABIP gap of 30 points. This is spanning the better part of a decade. That’s big, and that’s weird. It’s worthy of some kind of investigation.

Verducci’s article, to be clear, was missing something. He analyzed the Mets’ hitters, but he didn’t analyze the Mets’ pitchers. Since 2012, they’ve allowed the eighth-fewest runs at home. They’re in 17th in runs allowed on the road. And, since 2012, they’re 12th in BABIP allowed at home. They’re 28th in BABIP allowed on the road. Run scoring in general is harder at Citi Field. Turning batted balls into hits in general is harder at Citi Field. Mets hitters are hurt, and Mets pitchers get to benefit. But a question remains: why? Why is Citi Field so strange?

I’m going to tell you right now, I don’t have an answer. All I have is evidence that something is up. Let’s stick with that existing 2012 – 2018 data window. I hope you’re okay with that, because I’ve already assembled my spreadsheets. Over that span, relative to games on the road, Citi Field has reduced runs by 14%. It’s been the biggest run-suppressor in baseball. Interestingly, the home-run park factor is almost neutral. That was the intent when the fences were moved. But Citi Field has reduced BABIP by 8%. At home, Mets hitters have run a BABIP 30 points lower than on the road. That’s the biggest such difference in the league. At home, Mets pitchers have allowed a BABIP 21 points lower than on the road. That’s also the biggest such difference in the league. Citi Field doesn’t like allowing hits in play. Here’s all the proof you need:

Mets home games have had a BABIP about 25 points lower than Mets road games. That’s more than twice as large as the next-greatest negative effect. The other side isn’t too surprising — Coors Field is huge and it’s set at elevation, and Fenway Park has that ridiculous giant wall. You can talk yourself into understanding those. Not so much Citi Field. It’s not immediately apparent why what’s happening is happening.

This is our page for park factors. One contributing variable I can highlight: No ballpark increases infield flies more than Citi Field does. An infield fly is more or less an automatic out, which means infield flies are bad for BABIP. That helps to get us somewhere, but it still doesn’t give us a solution. Why not break down the batted balls that we’re dealing with? Above, you see the home/road BABIP split for all balls in play. Here’s the split for just grounders:

Citi Field reduces hits on ground balls, more than any other ballpark. How about now looking at just flies and liners? Remember that home runs are excluded.

Citi Field reduces hits on flies and liners in play, more than any other ballpark. Again, the other side makes sense. Coors Field allows a lot more air balls to drop in, while providing only a modest boost to grounders. Fenway Park doesn’t boost grounders at all; all the extra hits in play come in the air. Citi Field is just unusual across the board. It doesn’t matter how you hit the ball. The stadium doesn’t want you to reach.

Park factors are complicated. To really understand them, park factors are complicated. You’re dealing with wind, you’re dealing with temperature, you’re dealing with humidity, you’re dealing with batter’s eyes. I don’t know what it’s like to hit in Citi Field. I don’t know how it compares to other ballparks. Maybe it’s just tougher for hitters to pick up the spin, or something. I really don’t know, but I can point to something else. Not long ago, I wrote about Chase Field, which installed a humidor before the regular season. The main intended effect was to reduce how hard batted balls came off the bat. Based on the early evidence, mission accomplished: Chase Field doesn’t have much of a 2018 exit-velocity park factor. But let’s look at the same information again, highlighting a different ballpark. There’s a pattern here, something I initially regarded as a probable calibration error. Perhaps it’s not so.

All Statcast information comes from Baseball Savant. As you know, information exists going back to 2015. Let’s start there. For every team, here’s the difference between their home average exit velocities and their road average exit velocities, both for and against:

Citi Field, second to last. An average reduction of 1.2 miles per hour. Here’s the same plot for 2016:

Citi Field, tied for last place. An average reduction of 1.4 miles per hour. Here’s the same plot for 2017:

Citi Field, last place. An average reduction of 1.0 miles per hour. Here’s the same plot for 2018:

Citi Field, second to last. An average reduction of 1.0 miles per hour. At last, here’s the overall plot for 2015 – 2018:

Citi Field, last place. An average reduction of 1.1 miles per hour. At first I didn’t think much of it, because I couldn’t think of a good explanation. I still don’t really have a good explanation, but this lines up well with all the other information. Why might Citi Field act as such a hit-suppressor? Because it looks like it might well be an exit-velocity-suppressor. For some reason, batted balls in Citi Field don’t come off the bat as hard as they do in Mets road games. I know it seems like one mile per hour or so isn’t significant, but it can make a pretty huge difference over the course of a year. Just look at this year’s change in Arizona. Maybe it’s something about the baseballs, or maybe it’s something about the batter’s eye. Could be something else. But Citi Field has been working against the offense. Hasn’t mattered whether it’s been the Mets or their opponents.

I think I can mostly understand why the Mets’ hitters have felt it worse than the others: The Mets, over this span of time, have had a fly-ball-oriented offense, which has left them a little more vulnerable to the park effects. So it goes. Such things tend to be cyclical. What I’m most interested in understanding is why Citi Field seems to reduce batted-ball speed. When the Mets brought in the fences, they increased homers at the expense of other hits. That makes sense — the surface area of the field was reduced. But why does BABIP suffer so? Why does Citi Field look like such an anomaly? What’s happening in this part of New York that isn’t happening in the other part of New York? Again, I don’t have the answer. I’m not certain that anyone does.

But the Mets would be well-suited to figure something out. I’ll give you one more image before I go. Since 2012, here’s the home/road split in team winning percentage:

I mostly just put that in for a laugh. But either the Mets need to build a better team for the ballpark, or they need to understand what the ballpark is doing. This has all been going on long enough, and this is literally the place the Mets call home. One’s home oughtn’t be so mysterious.