In today's fantasy baseball environment, the most popular way for leagues to choose their rosters is to hold a mixed-league snake draft. However, this hasn't always been the case. The original incarnation of the game was to play in single-league (either American or National League only) auctions. The convenience of a snake draft and the preference to root for more familiar players has fueled the change.
While mixed leagues still dominate the landscape, there are nevertheless a significant number of fantasy enthusiasts playing in either American League- or National League-only single-league formats. What follows is a primer discussing the differences between mixed- and single-league formats. The focus will be strictly on league dynamics, although it is worth noting that mixed leagues mostly utilize snake drafts while single leagues are usually doled out via auction. Comparing and contrasting drafts versus auctions is a topic deserving its own discussion at another time.