A Strange, Profound Offensive Depression Gripped Wrigley Field This Year. Here's Why.

If you tuned into any Cubs games down the stretch this season, you probably heard an allusion or two by Marquee Sports Network play-by-play man Boog Sciambi to the weird weather patterns and drastic splits for the team at Wrigley Field this year. Behind the scenes, members of the Cubs themselves believe this was a real factor in their frustrating inability to consistently score runs at home this year, too. As a pivotal offseason looms, the team needs to properly evaluate its own players before deciding where to make key upgrades, and that means testing and fully comprehending those theories.

The basic math backs up both the seasoned observers and the cloak-and-dagger team apologists. Only at T-Mobile Park in Seattle did teams score fewer runs per game this year than at Wrigley, and at only four full-time parks--Oakland Coliseum, Busch Stadium, Kauffman Stadium, and Oracle Park in San Francisco--did a lower percentage of plate appearances end in home runs. That's all very unusual for the century-old ballpark, the offense-friendly reputation of which has sometimes been overstated but which has always played at least fair. It's drawn plenty of concern, because it would seem to distort the real production of players like Seiya Suzuki, Cody Bellinger, and Ian Happ. It even risks leading the team to give up too soon on hitters who go through periods of deep struggle, the way Pete Crow-Armstrong, Miguel Amaya, and--gulp--Christopher Morel did. Without getting to the bottom of the issue, it's very hard to figure out what the team should do to improve a roster that fell short of the playoffs for (in all important respects) the seventh straight season.

Let's try to do that, then. We've taken a surface-level measurement of the reality of the effect, but now, let's interrogate the nature of it. If the weather--temperature, air pressure, some funky interaction between new construction in the neighborhood and prevailing wind patterns or an overabundance of night games--were at fault, we would expect to see a wide gap between expected and actual results on batted balls. We would expect to see long fly balls die shorter, leading to long hits turning into loud outs.

That's somewhat in evidence, but only very imperfectly. As a test sample, let's take all batted balls at 95 miles per hour or harder, within a launch-angle band of 10-35 degrees. We're not using Baseball Savant's reverse-engineered formula, here, but we can call these Barrels just as credibly. If a ball is hit at least 95 MPH and is on a medium line or is a non-lazy fly ball, it was barreled, and it fits into a bucket of batted balls worthy of study for these purposes.

On such batted balls, this year, batters at Wrigley Field enjoyed the 19th-highest home-run rate, the 22nd-best BABIP, the 22nd-best OPS and the 20th-best ISO in the league. The park was, in other words, unfriendly to balls hit hard in the air, but they were closer to average than to the true bottom of the barrel. That doesn't mean it was the air quality or the wind knocking the ball down, though. The league's average exit velocity on those barreled balls at Wrigley was just the 24th-highest of the 30 parks. Using the specific speed and trajectory of each batted ball, Wrigley yielded more home runs and more triples (and fewer doubles, but by a smaller margin than the homers it added) than should have been expected. In total, 40.8% of barreled balls at Wrigley went for extra-base hits, whereas only 39.4% were expected.

No, the problem with the barrels at Wrigley was, there were radically few of them. No other park in the league saw fewer hard-hit balls in the air. The median number of such batted balls at a park, league-wide, was 736. At Wrigley, there were only 661. It's hard to blame the weather for the fact that hitters never generated the kind of batted balls weather hurts, in the first place. You could make the case, if you wanted, that the frigidity of April--there were 679 plate appearances at Wrigley that month in games in which the temperature was below 50 degrees, over 300 more than at any other park in the majors all year--made it harder for hitters to access their 'A' swings and blast the ball, but it's a bit of a reach. And even in those games, the park played essentially neutral, when the ball was well-struck in the air. It just didn't happen enough.

Let's consider another possibility, then. What if the Cubs themselves are driving this? This is a key thing to consider about the whole topic, by the way: If you're eager to excuse the Cubs hitters who didn't create enough home offense, you have to also reckon with the fact that the team's pitchers benefited from this phenomenon. Or else, maybe an underpowered Chicago batting order and a wily Chicago pitching staff helped create an environment that mirrored their own habits--a game with fewer truly zapped baseballs?

In short: it didn't happen that way. We do still need to think about the way these park effects quietly made Justin Steele, Jameson Taillon, and Shota Imanaga look better than they were, but it's not just about the Cubs being involved. As proof: the Cubs and their opponents combined to generate a Barrel Rate 4.8% higher on the road than the Cubs and their opponents at Wrigley. By far, that is the widest differential in MLB.

So, it's only fractionally weather that made Wrigley such a tough place to hit this year, and it's not the Cubs themselves, at all. What, then? We know it's not the ball. After all, the league now standardizes pre-game care for the baseballs, including providing a humidor in which the balls are stored before use. It's one safeguard put into place to blunt the differences between parks in terms of what was possible offensively.

My response to that is: Maybe the humidor sucks. Maybe the clubhouse staff are bad at using it, or Craig Counsell leaned on a dial back in April while having a conversation with Yan Gomes, and no one ever noticed he had changed the settings. I would not rule out that the ball has been deadened, inadvertently, by something in the chain of custody through which they pass at Wrigley Field. Hitters aren't lifting the ball as often, or hitting it hard as often, as they should be. It's hard to name a way that the humidor-stored baseballs and the surrounding environs could combine to kill the ball's coefficient of restitution, without making it fly less well, but maybe there's something there.

One way or another, though, hitters aren't generating good contact in the first place. That was the theme of this year at Wrigley Field--not good contact unrewarded, but surprisingly little good contact, period. Notably, the league is also hitting more ground balls than average at Wrigley this year--that is, the Cubs and their opponents hit more grounders there than when the team is on the road.

To be safe, I lopped off all games prior to May 1, and ran the same numbers. I then tried lopping off all games with a game-time temp under 60 degrees. No material changes whatsoever. Regardless of conditions, when at Wrigley, the Cubs and their opponents hit the ball harder (and hit it hard more often), hit it on the ground less (and concentrated more of their in-air contact in the best possible cluster of launch angles), and got much better results at other parks than at Wrigley.

This could be a random fluke, resolved by no remedy other than time and the slow erosion of memory. The data say, though, that there's more here than peculiar, persistent, despair-inducing weather patterns. The ball didn't do normal things at Wrigley Field this year. The team and the league should look closely at how to adjust that this winter, if possible. If not, the mystery of the extra ground balls and missing barrels will have to continue next year.