Have Games Become Less Competitive Since the Trade Deadline?
The Astros bludgeoned the Mariners on Saturday in a game that was over by the time the fifth inning was complete, when Houston owned a 12–0 lead and win probability odds of 99.9% (the final score was 15–1). That game marked the 19th time in August that a team had won a game by at least 10 runs, the most in any month so far this season — and we still have a week left to go before September. Naturally, the non-contenders that sold at the trade deadline or sat still have different priorities at this stage of the season compared to the postseason hopefuls. But how much of an impact does the deadline have on the game’s competitive nature?
You could try to measure this with run differential. Prior to the trade deadline, the average margin of victory in a game was 3.54 runs; since then, it’s gone up to 3.75 runs. But the average increasing by a mere 0.2 runs per game is not a monumental change. Similarly, you could look at two teams that held deadline fire sales — the Cubs and Nationals — and look at their post-July 31 performance. Chicago is down three runs and the Nationals 1.2 in terms of run differential per game, almost entirely due to pitching and defense. But those are extreme examples, and aside from Max Scherzer and Craig Kimbrel, the impact talent that both dealt away was mostly on the position player side.
Rather than just rely on anecdotal evidence, let’s take a probabilistic look at these outcomes. To test whether or not there is statistical evidence for the trade deadline creating measurable disparity, we’ll form two sets of discrete probabilities: one based on games through July 30 (prior to the trade deadline) and one based on games afterwards. Any games with a resulting run differential of greater than or equal to 10 runs will be grouped together.

Given the small increase in average run differential between the two periods, it’s no surprise that any change in probabilities is pretty small. But focusing on the left and right boundaries, you can see the differences that we’re looking for. While one-run games are still the most common, they’re happening a bit less frequently than they were before the deadline. The incidence of games decided by at least 10 runs, meanwhile, has gone from 3.9% of games pre-deadline to 6.0% after it. (Interestingly, run differentials in between the extreme values are pretty mixed.)


