One of the slightly confusing things about roller derby is the use of of the term League instead of Team. In most sports a League is an organization that stands above individual Teams, and is often thought of as being in control of rules making and game scheduling. However, in roller derby the term League has been appropriated to mean something slightly different.
It all goes back to the revival of modern roller derby. The first group that kicked everything off created a structure that would be copied by many. They created four Teams to play against each other. All four Teams were owned by the group so they, in essence, formed a League. Since they were the only roller derby group in existence, they were also the only League in existence.
As roller derby grew, and new groups formed, many of them mimicked the four team structure. The result was a bunch of tiny four team Leagues. This wasn't an issue at first because Leagues didn't really compete against each other.
However, as we all know, Leagues started to play against each other. And even though many Leagues might still have the old four Team structure, they also have what is now known as an All-Star, "A", or Travel Team. This is usually the team that plays against other Leagues.
As roller derby has spread, we now see some Leagues have abandoned the original four Team structure. Instead, they only have one Team. Are these groups supposed to be referred to as Team or League?
For the purposes of this list, each group, no matter how small, is considered to be a League. Even if the group has only one Team.
At this point we're stuck with the oddball usage of League. It's roller derby... just keep on rolling with it.