Does A Great April Predict Future Success?

As we head into the final days of April, there is no question which team has looked like the best club in baseball so far – the Texas Rangers are 15-4 and have scored more than twice as many runs (107) as they’ve allowed (52). Both their offense (26.5 runs above average) and their bullpen (14.3 RAA) have been the best in baseball, while their starting pitching (28.5 RAA) has been the second best in the sport. They’ve been nothing short of dominant, and given how well they’ve played, you might very well have concluded that they’re the best team in baseball.

They very well may be, but history suggests that an outstanding win-loss record in April is often not a sign of things to come, and even the best starts to the season don’t suggest that a team is truly set for a strong finish.

In order to come up with a list of teams began the season as impressively as the Rangers, we looked at every instance since 1974 where a team posted a winning percentage of .700 or better in at least 15 games. In total, there were 45 such instances, so it’s fair to say that you’d expect at least one team per year to win 70 percent of their games during the first month of the season.

The best start any team has had over this span is the 1984 Detroit Tigers, who began the year 18-2, outscoring their opponents 120 to 63 in the process. They went on to win 60.6% of their remaining 142 games and then won seven of their playoff games in route to a World Series championship. So, certainly, a hot start can be indicative of a team that is on its way to greatness.

The second best start since 1974 throws a little rain on that parade, however. The 1987 Brewers were nearly as good as those ’84 Tigers, going 18-3 in their first 21 games to start the year. They would then proceed to win just 73 of their remaining 141 games and ended the year in third place in the National League East. After posting an .857 winning percentage in April, their May-September mark was just .518.

There are more stories like the ’87 Brewers than you might expect. If we look at the combined totals for all of the 48 teams that won at least 70 percent or their games in April, we get a combined first month record of 765-264, or an average winning percentage of .743. Those same teams combined for a 3,598-2,990 record over the remainder of the season, which works out to just a .549 winning percentage. Or, to put it another way, the average team in this sample went 16-6 in April and then just 77-63 the rest of the way.

In fact, eight of the 45 teams that won at least 70 percent of their April contests would go on to lose more games than they won the rest of the year. No team had a more significant crash than the 1978 Athletics, who went 16-5 in April and then 53-88 the rest of the year. They had the best record in baseball in the first month of the season, and then followed it up with the third worst record in baseball over the final five months of the year. They stand as the only team of the group to manage a 90 loss season in the same year that they dominated in April.

We know wins and losses can be highly variable based on things that may not continue over the course of a full season, so I also decided to look at how these teams performed in terms of runs scored and runs allowed. I broke the 45 teams into quartiles based on their ratio of runs scored to runs allowed.

First quartile: 1.81 RS/RA, .584 May-September Winning Percentage
Second quartile: 1.49 RS/RA, .516 May-September Winning Percentage
Third quartile: 1.37 RS/RA, .527 May-September Winning Percentage
Fourth quartile: 1.24 RS/RA, .573 May-September Winning Percentage

The top 11 teams by RS/RA did perform the best of the four groups, winning 58.4 percent of their May-September games, but note that the teams with the worst run differential actually performed nearly as well, and significantly better than both groups ahead of them by ratio of runs scored to runs allowed. In fact, the correlation between April RS/RA and rest-of-season winning percentage is even lower (.19) than the correlation between April win-loss record and rest-of-season winning percentage, and in reality, both correlations are pretty weak.

While a strong start is certainly preferable to stumbling out of the gates, history suggests that we simply shouldn’t draw too many conclusions based on how a team looks in the first month of the season. Even with how dominant the Rangers have been so far, other teams have looked just as good and fallen on their faces as soon as the calendar turned to May.

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Dave is the Managing Editor of FanGraphs.
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Pretty sure the Brewers were in the American League in 1987.