Louis Baird "Pat" Duncan (October 6, 1893 – July 17, 1960) was an American professional baseball outfielder.

He played in Major League Baseball (MLB) from 1915 through 1924 for the Pittsburgh Pirates and Cincinnati Reds.

In 1921, the park (Crosley Field) was in its tenth season and no one had yet hit a ball over the fence without the benefit of a bounce.

The first ball to clear the fence on the fly was hit in late May by John Beckwith of the Chicago Giants of the Negro National League.

Then on June 2, with the last-place Reds playing the St. Louis Cardinals, Duncan dug in against left-handed hurler Ferdie Schupp with a runner on second and one out.