MLB

Your MLB Team Just Started Hot (Or Cold). How Much Does That Matter?

By Neil Paine

Apr. 5, 2023, at 9:05 AM

It warms this writer’s baseball-loving heart to see the MLB standings finally beginning to fill in anew this spring. Yes, that’s with an emphasis on “beginning” — we’re only a week into the season, after all. The temptation is always to overanalyze these super-early results, since it’s all we’ve seen of the fun new rules, new rookies and new roster configurations in games that actually count. But even though you shouldn’t get too excited (or down) about a team’s April results, there is still some signal in the early-season noise.

First, let’s look at how we would predict a team to finish the regular season if we knew nothing else except its record in April. Here’s a plot of April winning percentage versus full-season wins for all teams since 1996 (excluding 2020, when no games were played at all in April due to the COVID-19 pandemic):

There is a definite, if noisy, relationship between the two values — which makes sense, as good teams are more likely than bad ones to get off to good starts over a sample of nearly 800 team-seasons.¹ But however much a ballclub’s April winning percentage strays from .500 (on either the high or low side), we need to regress that figure back to the mean by about 62 percent to best predict the team’s final record. So if a team starts the year, say, 21-5 (an .808 winning percentage), we would expect it to finish the season with a 99-63 record (or a .611 winning percentage) rather than maintaining an .800 mark like it was the 1943 Homestead Grays or 1880 Chicago White Stockings and ending up with 130 wins.

Of course, we do actually know more things about a team early on than just its April record. For instance, we know how good the preseason prognosticators thought it would be — and while such forecasts are far from perfect, they do add extra information that helps temper a team’s expectations in the face of unforeseen results.² And what’s really informative for telling us how much stock to put in early records is to see how much those preseason priors move based on different April performances.

If a team was expected to go .500 and instead goes, say, 18-8 in April (a .692 winning percentage), suddenly we would expect it to finish the season with about 90 wins. If that same predicted .500 team goes 8-18 instead, we would expect it to finish with just 72 wins. Such is the power of a hot or cold start to the season. Yes, some of that is because the team gets to “keep” the record it had early on, even if its true talent was still just .500. But those expected records are still a few games better or worse than we would expect if it was all about banking away April records.³ A team’s early performance also tells us something real about how it will play going forward.

Now, there are limits to this. A team projected to win 60 games before the season would need to go 22-4 in April — a record no team has produced to start a season since the 1984 Detroit Tigers⁴ — just to be predicted to finish 81-81. (Sorry to be a wet blanket for when the Washington Nationals win their next 21 games.) However, for a team that was expected to be on the fringes of the playoff chase at the beginning of the month, a strong start could go surprisingly far toward solidifying its postseason positioning — and a weak one could put a damper on those hopes before they ever had a chance to develop.

Check out our latest MLB predictions.