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May 22, 2013 5:00 am
Why it pays to look at the weather forecast before starting a flyball pitcher at Wrigley Field.
One of the first axioms I learned when I wandered into the world of sports betting was to heed Wrigley Field’s winds. Wrigley’s proximity to Lake Michigan gave it a reputation for dramatically affecting fly balls, which would inflate or deflate the game over/under on runs. If the wind was blowing out, fly balls were expected to sail out as home runs, and the total would be unusually high. A low total typically meant that winds were blowing toward home plate, suppressing fly balls.
Vegas already knew this, which unfortunately added an additional dimension to handicapping Cubs home games. Amazingly though, this advice was extremely exploitable in fantasy baseball. An “@ChC” note next to my pitcher meant a trip to Baseball Weather Analyzer or Daily Baseball Data (two sweet resources) to examine Wrigley Field’s conditions that day. Flyball pitchers sat on blow-out days and started on blow-in days.
Chris Constancio of The Hardball Times investigated the effect of winds on HR/FB rates six years ago, and he observed statistically significant results in Chicago parks. I replicated his method on data from 2007 to the present and found that the Wrigley wind effect is stronger than ever. Over 508 games, here’s how pitchers performed in HR/FB rate, ERA, and slugging percentage allowed, split by Retrosheet’s wind field: