Lou Gehrig (left) and Babe Ruth (right) watch opposing pitcher Jackie Mitchell warming up before an exhibition game at Engel Stadium in Chattanooga, Tennessee on Thursday April 2, 1931.

From left to right: Lou Gehrig, Jackie Mitchell, Joe Engel, and Babe Ruth, at Engel Stadium in Chattanooga, Tennessee on Thursday April 2, 1931.

This is an autographed cover of a children's book about Jackie Mitchell, It is presumably specifically about the day of April 2, 1931 when at age 17 she consecutively struck out Babe Ruth and Lou Gehrig in just seven pitches at the start of her professional career, marking her debut on her home-town team, the Chattanooga Lookouts against the New York Yankees at the age of 17.