A Stark and Surprisingly Important Wrigley Field Park Effect, Hiding in Not-So-Plain Sight

Offense has been way, way down at Wrigley Field this season--for the Cubs, and for opponents, too. It's a strange phenomenon, but it seems as though the fickle winds, temperature patterns, and air pressure have buffeted fly balls and held up line drives, leading to a remarkably lousy year for hitters at the Friendly Confines. 

That's remarkable, sure, but it's not necessarily that important. Be sure not to give up on a Cubs hitter due solely to a lack of power generated this season, because there seems to be extra gravity pulling down their numbers in half their games. Next year, though, things are more likely to go back to normal than to persist this way, on a macro level. It's a one-year blip, as best we can discern or guess, even if it's an extreme and enigmatic one.

Go down a rabbit hole, though, and sometimes you end up in Wonderland. Thus, I find myself asking this question about a three-year park factor for Wrigley, and perhaps one with more staying power: Do lefty hurlers have a systematic advantage at the Cubs' home park?

Let me offer a disclaimer, right up front: There is a Justin Steele effect acting upon these numbers. Add Shota Imanaga to the mix this year, and yes, a couple of very talented lefty hurlers are oversampled in any comparison of the park's statistics based on handedness. Nonetheless, I believe what we're about to discuss is legitimate.

Here's a chart showing the weighted on-base average achieved by all batters against all left-handed pitchers at each MLB park, dating to the start of the 2022 season. If you don't see Wrigley Field right away, don't panic. You might just need to scroll down more.

Now, here's the same chart for right-handed pitchers.

Overall hitter- or pitcher-friendliness--most often, fence distances, but also things like elevation and weather--shape these lists as much as anything else. The pitchers who call a given park home can also have an influence. Don't try to use Steele or Imanaga to fully explain away this disparity, though. Facing a right-handed pitcher at Wrigley the last three years has led to exactly average production. Facing a left-handed one has led to the worst production in the league.

Flip this to view it from a hitter's perspective, and we can see something truly vexing going on. Only Camden Yards yields a bigger platoon differential for left-handed batters than does Wrigley Field. In other words, only that park has seen a bigger difference between the production by lefties against right-handed hurlers and that against southpaws. On the other hand, right-handed batters have actually been better against right-handed pitchers than against lefties over the last three years, making Wrigley the park that yields the smallest platoon differential for those hitters.

The effects run deeper than raw results. There's a significant gap in the chase and whiff rates lefties induce against lefty batters at Wrigley and the ones right-handed pitchers induce against those same lefty batters. Here's all 30 parks charted on those two stats in left-on-left matchups:

And here's the same chart for righty pitchers facing lefty batters:

Though it's an easy-to-pick-out outlier in the first chart, Wrigley is tough to see in the second, so for those struggling, it's part of the inoffensive thicket on the left, just above the average line for whiff rate on swings. Let's look at the same chart for left-handed pitchers facing righty batters:

And then for right-on-right showdowns:

This is weird, right? Except, isn't it also kind of understandable?

For decades--but especially for the last 30 years, since the team planted juniper bushes where there used to be unoccupied bleachers and then replaced the bushes with the batter's eye lounge--Wrigley has had an off-center batter's eye. The whole field is, in ways so subtle that some people miss it, quite asymmetrical. The wells in each outfield corner and the matching 368 signs in right- and left-center invite casual viewers to think of the place as symmetrical, but the well in left is longer and flatter, and the wall slopes away to a deeper gap in right-center, and the 368s are not at identical distances from the foul lines. The 400 sign is not in dead center field, but a bit to the right. The second tier of the bleachers and the manual scoreboard are slightly offset toward right-center. The cumulative effect of all this is a subliminal parallax that fools plenty of people, from fans to commentators--to hitters themselves. 

It also means that some left-handed pitchers' ball seems to come out of the crowd just off the edge of the batter's eye. That's not really the case, even to the extent that Jered Weaver's ball did appear to come out of the rockpile at Angel Stadium during that stellar righthander's heyday. It's just that the slight misalignments and not-quite-symmetries invite a hitter to experience a slight visual distraction. As a hitter, you want to keyhole a pitcher. You want a tight focal point with plenty of visual contrast. Some lefties can refuse a hitter that at Wrigley.

Photo By User Thechitowncubs on en.wikipedia

Again, unless a pitcher is about 11 feet tall and uses a crossfire delivery from a three-quarter slot, they're not actually throwing the ball from a place where the hitter is likely to lose it in a light-colored shirt in the crowd. It's more insidious than that. Still, the effect appears to be real. This has been mentioned by some hitters visiting Wrigley over the years, but it doesn't always show up in the numbers. Maybe it's another fluke, like the shifting weather patterns--albeit one that has had an impact across multiple seasons. Maybe it's a function of the league as a whole working harder by the day to create tough release points for hitters, and it's just been magnified a bit by the presence of Steele and Imanaga on the Cubs roster recently.

The effect isn't completely illusory, though, just like the park's symmetry isn't completely real. Camden Yards's huge platoon differential for left-handed batters is there because of its cavernous left field, with the deep, high fences. PNC Park also has a big platoon differential for lefties, because of its very deep left-center alley. Minute Maid Park (Crawford Boxes) and Tropicana Field (that very shallow left-field corner, with the cutout in the wall, where Isaac Paredes became famous) have the smallest platoon differentials for lefties. The takeaway there is that much of the variance can be explained by the ability to hit opposite-field home runs, or not.

The biggest platoon differential for right-handed batters, unsurprisingly, is at Fenway Park, where righties can't count on hitting homers to right and right-center. The smallest one, other than Wrigley, is Yankee Stadium, because Aaron Judge could hit a ball out to right-center there with his bare hand if he really had to. These are all explained by park dimensions, and the extremes all correspond with parks that are highly asymmetrical. That Wrigley is at one end of the spectrum for lefty batters and the other end for righties, with fairly symmetrical dimensions, tells us something else is going on. The differences in the way batters see the ball, resulting in more bad swings against lefty pitchers than against righty ones, tells us something else is going on. 

One way or another, a visibility issue has crept into the equation at Wrigley. Maybe hitters don't want to mention it, or even admit it to themselves, because of the psychological games pitchers might play in the wake of such an admission. Maybe they're not even fully aware of it. But right-handed batters are doing better against right-handed pitchers than against lefties, and left-handed batters are experiencing a huge platoon effect going in the normal direction. That's despite dimensions and wind patterns that, if anything, slightly favor lefties hitting against lefties, not righties hitting against righties.

In the short term, the Cubs should keep stockpiling left-handed hurlers. It's almost certain that they're aware of this phenomenon, whether they set any store by it or not, and it might be part of why they elected to retain Drew Smyly on a surprisingly rich deal two winters ago. It might be why they made themselves the high bidders on Imanaga last offseason. They can seize a bit of an edge, while whatever conditions have led to this trend perdure, by having more southpaws on the mound than their opponents at home.

Beyond that, though, it's less clear what they should do. This feels like an unmanageable enigma, especially from the offensive side. Whether this is a component of or a mere coincidence with the broader offensive depression that settled over Wrigley this year, it's going to be hard to find a reliable plan for dealing with this effect when setting a lineup or building a roster. If we accept that this is just about the way the ball is carrying, the implication would be that it's not carrying at all to left field, turning Wrigley into a version of Walltimore or Pittsburgh, but that it is carrying exceptionally well to right, just like it does at Yankee Stadium and at Truist Park in Cobb County, Georgia. The data doesn't back that up, and neither does the historic pattern of play at Wrigley.

The solution is just to build a great roster that wins with or without the help of small environmental factors, but since the Cubs haven't shown the financial gumption to do that lately, they face a daunting challenge in the coming months: construct a roster that can compete with the Brewers and Dodgers and Phillies and Atlanta, while dealing with a couple of inscrutable park factors that will complicate their player evaluation and their projections for 2025 and beyond.