The League Associations option (Game Menu >> Current Game section >> League Associations) is where you can create and administer league associations in your game:

League associations enable leagues to interact in specific ways (e.g. trading between them, a common draft pool, a post-season featuring clubs from the member leagues, etc.), while allowing each league to retain its unique settings and characteristics, such as active roster size, secondary roster size, and so on. There are two game screens related to league associations:

• Association Setup and Options
• Association Overview