I think that it should be like this:

1 Battle Crew
1 Topical Crew
1 Open Mic Crew

That way each person can participate in 3 crews of all different genera's. If you have a crew with Topical and Battle then you can only have 2 crews.

Token's idea was pretty good to, left out Topical though, which seems to be getting a little bit more popular.

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