I found this.
A butt is an archery shooting field, with mounds of earth used for the targets. The name originally referred to the targets themselves, but over time came to mean the platforms that held the targets as well. For instance Othello, V, ii, 267 mentions "Here is my journey's end, here is my butt". In medieval times, it was compulsory for all yeomen in England to learn archery; see for example An Act concerning shooting in Long Bows, passed in the third year of Henry VIII's reign.