Friday marks the start of the third season of MLB Players' Weekend, the annual August promotion which, as you probably know, features players on all 30 teams wearing nicknames on the back of their jerseys, instead of their surnames (or in the case of the Yankees, instead of nothing at all).
What you might not know, however, is that a decent number of MLB players, including at least two Hall of Famers, wore nicknames on their backs well before the advent of Players' Weekend. These instances can be broken down into three major categories, so let's take them one at a time.