Jacob Henry "Ol' Jake" Eisenhart (October 3, 1922 – December 20, 1987) was an American left-handed pitcher in Major League Baseball who appeared in one game for the Cincinnati Reds in 1944.

Eisenhart is one of many ballplayers who only appeared in the major leagues during World War II.

After attending Juniata College,[1] he was signed by the Reds to a 30-day trial contract,[2] but his only big league action came on June 10, 1944 in a home game against the St. Louis Cardinals at Crosley Field.

Eisenhart walked the first batter he faced, George Fallon, then got the last out, retiring opposing pitcher Mort Cooper on a foul out.

[2] Eisenhart also served in the Army during World War II,[4] and toiled three years in the Philadelphia Athletics organization, but never made it back to the major leagues.