Chicago Cubs: What run differential tells us about trends of success

Understanding run differential

The most basic meaning of run differential is understood as the difference between the number of runs a team scores versus the number of runs they allow. The Chicago Cubs, for example, have scored a total of 200 runs this season, while allowing 146 runs. This gives them a total differential of +54.

According to Fangraphs, the Cubs currently sit in fourth overall in baseball, scoring 5.41 runs per game. The team has allowed the eighth-fewest runs per game, at just 3.95. At some point down the line, stat nerds figured out that roughly ten runs were equivalent to one victory. Fangraphs has a measure known as R/W or runs per win. In 2017 the R/W was 10.04, the highest in the last decade. This season, thus far, the R/W is 9.69. So, what does this all mean?

In an attempt to take this data and apply it to a projected number of wins over a season, you must start at the midway point, or .500. As the Cubs have played 37 games, halving it would give you 18.5, so roughly 19 wins. Making the run differential divisible by ten would project 5.4 more wins, giving them, approximately 24 wins. As it were, they are 21-16, meaning they are playing below their projections at this point.

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The 2016 season saw the Cubs finish with a run differential of +252. The team finished 103-59 that season, in route to winning the World Series. Strangely enough, the team played under their expected value. The Cubs expected win total that season was 106.

Unsurprisingly, the Cubs finished 2016 first overall in run differential average at 1.6. The next closest team, Boston Red Sox, finished 0.5 runs behind the Cubs.

Last season, the Cubs arrived back to earth finishing with a still impressive +127 run differential. They finished 92-70, which is not far off from their expected finish of 93-69. Unsurprisingly, the run differential average was down to 0.8. However, it was still a top ten finish. The two eventual World Series opponents, Houston Astros, and Los Angeles Dodgers finished tied for second respectively at 1.2.

Arguing against run differential

For every statistic based on logic, there is a counterpoint to its overall effectiveness. In Major League Baseball some teams have a negative run differential total, yet still, find themselves at a winning record. Also, some teams who possess a negative record somehow have a positive differential.

The National League West is a perfect example of this. The Colorado Rockies currently sit at 22-19, good for second in their division. They have a -20 run differential. The Los Angeles Dodgers, for example, are 16-24 and 5 1/2 games behind the Rockies and have a -1 differential.

In this case, the Rockies record should be 19-22, meaning they are still playing above their projections, despite such a porous run differential. It is understood though because the Rockies have not only been involved in many high-scoring affairs this season so far, they have lost a couple of times spectacularly, creating that skewed number. It is an argument against basing run differential on a team’s overall success.

The difference here, in comparing the Cubs with the Rockies, is that the Cubs have just four more wins than the Rockies, however there is a +74 run differential in the Cubs favor comparing the two teams. The Cubs, in theory, should have seven more wins, comparatively. Once again, another argument against using run differential as a measuring stick.

Projecting the rest of season

For the Cubs, their offense continues to flex its muscle. The team is now in a stretch in which they have scored 10+ runs in three of their last six contests. They scored eight runs in another of those games.

Using their run differential of +127 in 2017, let’s project them out to a final +130 differential by the end of the season. The team finished with 92 wins in 2017. In using the formula, the Cubs would finish the 2018 regular season at 94-68 which would expectedly win the division once again.

Projections can be fun, too, however. Due to the pace, the Cubs are on now, the club projects out to +216 through 148 games played. Let’s add another 15 runs to that total to project out the remaining 14 games, and it would give the Cubs a run differential of +231, only 21 runs shy of their 2016 mark.

To measure the season as a whole, we would begin our projection at 81 games, half of 162. Dividing the run differential by ten, it gives the team roughly between 22 and 23 more wins. By way of numbers, it would give them around between 103-104 wins. These numbers would suggest the Cubs are playing at their expected value.

Next: Cubs treading water away from Wrigley Field this season

Naturally, the 2016 season was an outlier. It may be difficult to project the Cubs to continue this torrid offensive banger they find themselves on, however, at the level, they are playing they continue to set themselves up nicely for another 90+ and maybe 100-win season once again.