TRIVIAL PURSUITS: What Was the Biggest Baseball Change Before the DH?

January 11, 2011 ( - On this day in 1973, the owners of America's 24 major league baseball teams vote to allow teams in the American League (AL) to use a "designated pinch-hitter." 

Some argue that the introduction of the designated hitter (Rule 6.10) marked the biggest rule change in major league baseball since 1903 – when what change was made?  

Answer:  When it was decided that foul balls would be considered strikes.