Where does the term to beat a granny come meaning your opponent is left with seven balls at pool?

The term "to beat a granny" in pool refers to a situation where one player leaves their opponent with only seven balls remaining on the table, often implying that the opponent is in a difficult position. The term humorously suggests that even a beginner or someone perceived as less skilled, like a grandmother, could win against a player who has made poor strategic choices. It highlights the contrast in skill levels and the unexpected outcomes that can occur in the game.