How Sports are (Analytically) Different in the Bubble

Most of the world’s major sports have resumed, or will pick up again soon, in some form or other. But a lot is different, with most leagues forming one or more bubbles, often excluding fans, limiting travel, and tweaking things like officiating rules to better maintain social distance.

Many of these changes have second-order effects. For instance, the “Cincinnati” tennis event requires that players fetch their own towels–which probably slows down play–but has no fans–which could accelerate it. We’ll soon have enough data to draw some preliminary conclusions about the overall effect of the new rules on pace of play.

Some of the issues that arise when a league moves into a bubble apply across sports, like home-court advantage. With that in mind, I’m gathering evidence of how sports are playing differently in our time of social distance. I’ll try to keep this post updated as we learn more. The comments are open, so you can contribute any demonstrated effects that I haven’t listed here. (Or similar effects in other sports.) You can also tweet at me.


So far, home-field advantage is almost non-existent. Historically, home teams win about 54% of games.


NBA offenses can’t stop scoring. Refs are calling more fouls, and fewer off-court distractions get in the way of making shots.

The WNBA is showing the effects of a league full of fresh legs, and has displayed a record-setting pace of play. And despite playing on the same court every night, there is a marked home-court advantage.


Fighting is up! Lucky NHLers–most of us don’t go to work where it’s culturally acceptable to hit people.


Home-field advantage is reduced, but it still exists, even behind closed doors. A recent paper (summary / PDF) notes that refs have been more lenient than usual toward away teams. That tallies with long-held conventional wisdom that home-advantage stems from officiating bias, which is driven by noisy, partisan crowds.

Speaking of officiating, refs were more likely to grant penalty kicks, but despite the quieter environment, penalties aren’t converted any more often.

For more detail on home-field advantage in various leagues since the restart, here is a valuable Twitter thread from @recspecs730.


I’m keeping tabs on whether match results are less predictable than usual. (They are, but we haven’t really seen enough to be sure.) Other than that, it’s still speculation. We’ll know more after “Cincinnati,” and much more after the US Open.