Blake Street Stroll: How much stock should we take in run differential?

Patrick McDermott

The Rockies are fourth place in the NL West and yet they lead the division in run differential. Does it matter?

In yesterday’s Rockpile, Jordan Freemeyer pointed out that the Rockies are leading the division in run differential despite currently sitting in fourth place in the division. This led me to wonder, does run differential matter?

Run differential is certainly an inexact stat. A logical thinker would believe that a team with positive run differential at the end of a season is better than a team with a negative run differential. The logic is simple; score lots more runs then the opponent and give up lots less. However, there are many factors that are not considered in this logic.

Baseball is unique in that a team’s success is largely based off how their starting pitcher performs that day, hence the old saying, "Momentum is only as good as tomorrow’s starting pitcher." In baseball, a team can get a great pitching performance and win 15-0 or they can win 2-1. The same can be said in reverse for a team that experiences a bad start.

Since a baseball game is rarely determined by the same score on consecutive days a team can have a rather large run differential, either positive or negative, but it does not necessarily mean the team is good or bad. Take the ’07 Arizona Diamondbacks for example, they won 90 games and even won a playoff series despite having a -20 run differential.

The ’05 San Diego Padres won the division at 82-80 despite a -42 run differential and the ’97 San Francisco Giants made the playoffs and won 90 games despite a -9 run differential. So run differential isn’t a valid statistic because of this, right? Consider this, since the Wild Card era began in ’95 only the three previously mentioned teams made the playoffs with a negative run differential. That’s 133 playoff teams with positive run differentials and three with negative. And interestingly enough, all three of those teams came out of the NL West.

Also consider that of those 136 playoff teams, only nine made it to the postseason with a run differential less than +50. In other words, run differential can be a very telling statistic for a good ballclub.

At +34 run differential Pythagorean W-L has the Rockies at 41-35, a better mark than their actual 38-38 record. Pythagorean W-L is a formula created by Bill James that calculates what a team’s record should be based on their run differential. It essentially can tell you if a team is extremely lucky or unlucky. But luck can only explain so much. Perhaps a team is just unusually clutch, or they have great starting pitching and a mediocre offense so their run differential is close to even, and yet they are 25 games north of .500. It’s difficult to say exactly how much or how little run differential means, but typically a good team has at least a +50 run differential.

Run differential is certainly not a perfect stat, neither is Pythagorean W-L, but in general, trending towards the positive in both those stats is a telling sign of how good a ballclub really is. In the Rockies case, they are trending in the right direction and that certainly bodes well for the rest of their season. Is run differential the ultimate judge of a team’s success? It’s hard to say, but for the Rockies, +34 is better than -34.

Baseball is beautiful because it simply cannot be predicted, but that doesn’t mean that statistical and historical trends should be ignored. The Rockies, purely based off of run differential are headed in the right direction and are legitimately a good team.

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