His professional umpiring career began in 1888, and after spending a couple of seasons in the minor leagues, he was promoted to the major leagues as an umpire in 1890. Emslie was nicknamed "Wig" due to his premature receding hairline, which was a result of the stress of umpiring games single-handedly in the rough-and-tumble 1890s; he was derisively called "Blind Bob" by the New York Giants following his role in the infamous "Merkle's Boner" play during the National League pennant race. The play involved a force out when a Giants player stopped running to second base upon seeing that the game's winning run would score.