From SABR member Cyril Morong at Cybermetrics on November 7, 2019:
I used data from Retrosheet and Baseball Reference (the one year missing is 1903 since neither site has OPS allowed for the pennant winners). This is based on regular season OPS differential.
So this year was the 4th biggest upset.
Of course, maybe late season OPS differential could be a factor. But as I recall, there is research that says if a team is hot late in the season it does not necessarily translate into success in the post-season.
Read the full article here: https://cybermetric.blogspot.com/2019/11/biggest-world-series-upsets-by-ops.html
Originally published: November 11, 2019. Last Updated: November 11, 2019.