Road teams are (surprisingly?) benefitting from MLB’s extra innings rule

When Major League Baseball instituted their new extra inning rule ahead of the pandemic-shortened 2020 season, it was not universally praised. No more would we see epic 19-inning games that featured utility infielders locking down a potent lineup in advance of his team winning a game in dramatic walk-off fashion.

Nor would we see a rookie shortstop in his Major League debut be a part of a dramatic, 20-inning marathon victory during an improbable playoff run.

Yes those are memories etched forever in the memory banks of every Phillies fan, and we won’t see their likes again unless the rules changes, but the reason for the rule was understandable. In a desire to limit person-to-person contact on the field, Commissioner Rob Manfred green-lighted the rule in which a runner is placed on second base at the start of every extra inning, and it has continued into the 2021 season, yielding some surprising results.

CONVENTIONAL WISDOM

When this rule was put into place, my assumption was that home teams would have a distinct advantage in extra inning games. By hitting in the bottom of the inning, home teams would be able to play for one run if the visiting team did not score in the top of the inning by sacrificing the runner to third and giving themselves a chance to win with a fly ball or well placed grounder. The road team, on the other hand, could not play for just one run. They would have to score as much as possible, knowing that if they played for just one run, the home team could at the very least match it.

I expected for this to be a big deal and for home teams to pile up the extra inning wins.

Boy, was I wrong.

THE DATA

When I mentioned this hypothesis on Twitter earlier this year, a couple Phillies fans thought otherwise and, thanks to the hard work of Shelby Fabian (@bichon1200), they were proven correct.

In 2020, away teams were 41-35 in extra innings (.539 winning percentage), with an average margin of victory of 1.59 runs. Of course, that’s a small sample size. The 2021 data would certainly even things out and show that home teams really do have the advantage, right?

Nope!

This year, away teams are 101-89 (.532) in extra innings, with an average margin of victory of 1.71! Of course, how do we know that the so-called “good” teams haven’t been stuck playing on the road a majority of the time and the “bad” teams were the home teams? Well, Shelby’s data lays it out pretty succinctly.

No matter the skill level of the team, the road team has the advantage and, in the vast majority of cases, the new rule has had the desired effect and ended the game after 10 innings (140 out of 190 extra-inning games this year, through Tuesday), 73.7%.

WHY IS THIS HAPPENING?

There are a number of possibilities, but a couple were outlined by two other Phils fans on Twitter who initially challenged my assertion that home teams would have the advantage under the new rule.

A standard run expectancy matrix bears this out.

As outlined by Fangraphs, teams would expect to score 1.068 runs in an inning when they start an inning with a runner on second and no one out. When a team bunts the runner to third with one out, that number drops to 0.865. Road teams simply aren’t doing that in the top of the 10th or 11th inning, knowing the home team would be able to match it. Instead, road teams are taking their chances to score multiple runs in the top of the inning and, as born out in the matrix, that generally leads to scoring more runs and, in this case, winning extra inning games.

One also cannot discount the psychological aspect of the home team almost always facing a one-run deficit in the bottom of the inning, even if they can play for the tie by scoring one run. Baseball players are human, after all, and the pressure of hitting down a run as opposed to with the score tied likely isn’t a non-zero factor.

CONCLUSION

But perhaps it’s not just the new rule. Perhaps road teams have always had the advantage in extra innings. Shelby did crunch the numbers for a few recent seasons.

So there you have it. It would appear the new rule has taken away some of the homefield advantage, at least as far as data over the last five years are concerned. At the end of the day, over the last three years, you want to be the road team if you’re playing bonus baseball.