Page "Babe Ruth" Paragraph 6

Another rules change that affected Ruth was the method used by umpires to judge potential home runs when the batted ball left the field near a foul pole.

Before 1931, i. e. through most of Ruth's most productive years, the umpire called the play based on the ball's final resting place " when last seen ".

Thus, if a ball went over the fence fair, and curved behind the foul pole, it was ruled foul.

Beginning in 1931 and continuing to the present day, the rule was changed to require the umpire to judge based on the point where the ball cleared the fence.

Jenkinson's book ( p. 374 – 375 ) lists 78 foul balls near the foul pole in Ruth's career, claiming that at least 50 of them were likely to have been home runs under the modern rule.