What Does Opening Day Tell Us?
Not too much, unsurprisingly.
MLB’s Opening Day finally arrived Thursday, and it was a fun celebration of the sport and its shiny new rules (which seemed to achieve their intended purpose, as they did throughout the spring). It’s more fun, of course, when your favorite team wins — though the losers of Game #1 can always say there are 161 left to make up the difference in. But how much do we really learn from Opening Day anyway?
For this (admittedly silly) little exercise, I looked at every team’s first regular-season result — win or loss — since MLB expanded to 30 teams in 1998, excluding the pandemic-shortened 2020 season, and tracked how the winners and losers of Opening Day ended up doing over the course of the entire season.
As we might expect, Opening Day winners end up winning more games on average per season than their losing counterparts. And that difference is more than just what can be explained by banking 1 extra tally in the W column. If a team won its first game and went .500 over the remaining 161 games, that team would only have 81.5 expected wins; our observed sample of Opening Day winners checks in with 82.5, suggesting that the group of teams who start the season with a win are slightly better than average over the rest of the season as well. (But only slightly.)
Oddly, though, this edge does not seem to carry over into the postseason. While we’d expect the average team since 1998 to have a 1-in-30 (or 3.3%) chance of winning the World Series, our group of Opening Day winners went on to take the championship just 3.1% of the time. By contrast, the Opening Day losers got the last laugh more often — they won the World Series 3.6% of the time.
I have no grand theories as to why this is, aside from the noise that can crop up in 24 seasons’ worth of data when only one team per year can win the championship. Looking at eventual World Series winners since 1998, 11 won on Opening Day and 13 lost, which explains the difference in World Series probability from the preceding table. Is that a meaningful difference at all? No. (Flip one eventual champ’s opening result from a loss to a win, and there’s zero difference in World Series success rate between the groups we looked at earlier.)
But it does allow hope to spring eternal for fans whose teams lost on Thursday. Because, technically speaking, recent teams who got off to that kind of start actually do better in October than those who won their openers.