Appeal to spectators for maximum approval, as in He peppers his speeches with humor and wisecracks about his opponent, clearly playing to the gallery. In this term gallery refers to the cheapest seats in a British theater and hence the least sophisticated audience. [Late 1800s]

To direct a performance toward less sophisticated tastes; by extension, to attempt to gain approval by crude or obvious means: “The cast of the play was a decidedly mixed bag of youthful method actors and old hams who played to the gallery.”