Through 21 games at Wrigley Field this season, the Cubs and their opponents have totaled 188 runs — 8.95 per game. Through 13 road games, the total is 131 runs — 10.08 per game.
That the Cubs and their opponents are combining for only 88.8% as many runs in Wrigley as they are in Cubs road games is consistent with recent results, but not with Wrigley’s history and reputation as a haven for hitters.
Focusing on runs per game is a shortcut toward measuring park effects. Park factors used in metrics such as weighted runs created plus, weighted on-base average and wins above replacement are more complex to account for unbalanced schedules and teams having different mixes of road parks.
Still, a look at runs home and away can give us an idea of Wrigley trends.
During the Cubs’ run of six consecutive seasons above .500, runs park factors listed at ESPN.com have been .950 in 2015, followed by .874, 1.131, 1.079, .931 and .741. That means runs per game last season at Wrigley were only 74.1% as high as in Cubs road games.
Contrast that with the last time the Cubs broke .500 six seasons in a row (1967-72). Starting in 1967, runs park factors were 1.032, 1.300, 1.123, 1.430, 1.216 and 1.270. At the 1970 peak, 1.43 runs were scored at Wrigley for each run in Cubs road games.
Each season of the earlier period brought more runs per game at Wrigley than on the road. In four of the six seasons starting in 2015, there were fewer runs per game at Wrigley than in road games. So far, 2021 has been more of the same.
There are a number of possible explanations, including wind patterns and park construction, such as the huge new scoreboard.
Ballpark openings and closings also make a difference. Park effects exist in comparison with other ballparks. The Cubs of 1967-72 didn’t get to hit in Coors Field, an extremely friendly park for hitters. The Cubs of today don’t have to hit in the Astrodome, an extremely friendly park for pitchers. Those and other changes make Wrigley less hitter-friendly today in comparison to other parks.
You can see the difference in individual stats. As a Cub, Anthony Rizzo’s .905 OPS at home is a big step ahead of his .822 on the road. The same goes for Willson Contreras (.859 at home vs. .763 away).
But Kris Bryant has been much the same hitter at Wrigley (.900) as he has been away (.890), and Javy Baez has been better on the road (.792) than at home (.765).
That mix is a change from the earlier Cubs, whose big hitters had huge home-road splits. Billy Williams (.917 at home, .817 on the road), Ron Santo (.914, .760) and Ernie Banks (.886, .773) all had more extreme splits than Rizzo and Contreras.
The older generation sometimes is accused of not showing up on the road, but much of the difference comes down to park effects. The Cubs of today hit in Wrigley confines not as friendly as they once were, but they also hit in road parks that don’t stifle offense as much as those of yore.