This article will explain the maximum number of teams that can be joined in private and regular public leagues.

Public & Private Leagues:

Managers, will have a limit of eight teams or leagues to join in any combination of private or custom, Head-to-Head, Rotisserie or Fantasy Points, with a single Yahoo! ID.

Pro Leagues: 

Managers will be able to join an unlimited number of Pro Leagues. These teams will not count toward the 8-team limit for private/public leagues.