Don’t be fooled by the Blue Jays’ and Yankees’ run differentials

If you want to raise the blood pressure of two fan bases, just utter the phrase “run differential” and it will elicit a polarizing result from supporters of the Toronto Blue Jays and the New York Yankees. These two teams are at opposite ends of the spectrum, yet one is atop the American League East and the other is on the outside looking in.

Earlier this week, Yankees broadcaster Michael Kay referenced the run differential metric in his argument that the “Blue Jays were not a first-place team”.

“If you look at the run differential, the Yankees’ run differential is +105. The Blue Jays, after a 12-5 win, finally got in the positive yesterday. They’re +4. Do you realize they should be a .500 team because of a +4 run differential? And the Yankees should have at least four or five more wins with a +105 run differential.”

He’s not wrong that the Blue Jays seem to be over-performing and the Yankees are under-performing, but the run differential number alone doesn’t tell the full story.

Heading into Friday’s games, Toronto had a +9 run differential, while New York had a +100 run differential. The Yankees have outscored the Blue Jays by 91 runs this season and they have one fewer win. How could this be? What witchery is happening to Toronto to make this happen?

It’s quite simple: when the Yankees win, they win big. When they lose, they lose by a small margin. Conversely, the Blue Jays play plenty of tight ball games and typically win by a small margin. But when the Jays lose, they lose handily. That’s why the run differential is so lopsided, yet the Blue Jays have a better record than the Yankees.

Average runs per win and loss (Blue Jays and Yankees)

On average, the Blue Jays win their games by 3.41 runs and they lose by 4.16 runs. The Yankees, however, averaged 4.37 runs in their victories and 2.82 runs in their losses. The Blue Jays win lots of close games, and the Yankees lose lots of close games. The Blue Jays lose in blowout fashion often and the Yankees win in blowout fashion often.

And then when you break it down by monthly splits, you see the Yankees absolutely destroyed the competition in March, April and May, but came back down to earth on June 1. Meanwhile, the Blue Jays got over their disastrous opening of the season to post positive run differentials since May 1.

The Blue Jays have arguably had a tougher schedule than the Yankees in the first half as well, which may have skewed the win and loss totals for both teams.

Run differential by month (Blue Jays and Yankees)

Marc Normandin also had a great thread on this very subject earlier today.