In sports, we often hear the phrase, “defense wins championships,” and specifically in baseball, “pitching wins championships.” The other night on an ESPN baseball telecast, analyst Steve Phillips was taking that very argument even further, asserting that low ERAs are more important that high offensive production when it comes to winning championships. While there is no doubt that lower team ERAs help win games and playoff series, I am skeptical of much of what comes out of Phillips’ mouth, so I set out to check his hunch.
First off, to get into the playoffs and have a shot at the League Championship Series, teams have to win in the regular season. Taking a quick look at some regular season stats from the last 20 seasons and how they correlate to regular-season wins, season run differential (average runs scored minus average runs allowed) comes out on top. If you’re concerned about the differences between the AL and the NL, the only noticeable difference is that offensive runs per game tend to be slightly more important in the AL than in the NL.
*Coefficients closer to 1 represent stronger correlations
Stat Coefficient Wins+/Run
Run Differential 0.92 16
ERA 0.63 13.5
Total runs scored per game 0.56 13
This tells us that, of these three team stats, it’s the run differential that best explains teams winning games, and making it to the playoffs. Also, ERA tends to explain total wins slightly better than run scoring. Hey Steve, you might be on to something here. Winning championships, though, is a different story. The unpredictability of five or seven-game series does not often distinguish teams that have only marginally better ERAs or run differentials.
Observing the logistic correlation between just the playoff teams’ season stats versus winning league championships exhibited some interesting results over the last 20 years—not counting 1994, obviously, because of the strike.
In the American League, the best correlation to which team won the ALCS was total season wins, followed closely by run differential and ERA. Each of these was an excellent indicator of which team won, all being significant at the 5% level. However, runs per game did not have any predictive power over which team won the ALCS.
In the National League, none of the correlations were particularly strong, but again season wins came out on top, followed this time by ERA then run differential. However, no correlation was significant at even the 30% level. Runs per game stayed consistent, showing almost no correlation to NLCS winners.
There are some important things we can take from this study. Teams that make the playoffs and give themselves a shot at the championship are likely to be teams with healthy, positive run differentials. Because run differential implies both high run-scoring and low ERAs, these stats also logically correlate to winning.
Once we get to the playoffs, the best predictors for League Championship Series Winners are—aside from total season wins—ERA and run differential, which both are much more important than offensive production. Basically, teams that win the regular season win in the playoffs, and teams with low ERAs and good run differentials win championships more consistently than teams with greater run production.
When building a team to win a championship, the past has shown that healthy run differentials, when driven by lower ERAs, are the keys to winning the League Championship Series. I would like to give Steve Phillips a gold star for his always on-target gut instinct. Please sense the sarcasm.
Reading into the Numbers 
Quote from Moneyball: “The playoffs frustrate rational management because, unlike the long regular season, they suffer from the sample size problem.”
Think 2006 Cardinals, 2007 Rockies — the team that is healthy and running on all cylinders can make up for a less than stellar regular season by winning a couple short series in october.
Sure, run differential can be a good predictor of success, but don’t overlook a team’s play down the stretch.
Of course! The best teams have an extremely high chance of making the playoffs, versus a much less-sure chance of winning a playoff series. The correlation of any statistic (other than wins) to winning playoff series is never as good that same correlation to season wins. In a short series, team health and randomness play a huge role in which team comes out on top.
For example, as a model, a team that randomly wins 60% of it’s games has a 90% chance to win at least 90 games. Conversely, after making it to the playoffs that same team has about a 70% chance to win a 7-game series. While 70% is a good percentage, it’s not nearly as high as the chances of having a good regular season.
Michael Lewis’ point in Moneyball is that a team designed to win over the long haul doesn’t necessarily have an advantage in the playoffs. In my opinion, playoffs in most sports are a complete crapshoot, and declaring the winner of the World Series the best of the league is often simple-minded and erroneous.
Playoffs should be taken for what they are. A fun, exciting, end-of-the-season tournament which – more often than not – crowns a champion when there is a more-deserving team somewhere else in the league.
[…] Wins from Run Differential In a previous post, I discussed the importance of run differential to winning ballgames. Run differential (runs scored […]