There are high school football teams a few miles from The Dialer that draw better than the Zips. IIRC there were college football games at the HoF that drew 30k.
I saw the Cleveland Force draw bigger numbers for exhibition outdoor soccer games, trying to get into an outdoor league, and a lot more people than were there Saturday night. What held him back from moving outdoors was the artificial turf. The Force had quite a few home sell outs (18,000+) for human pinball (indoor soccer) (in Summit County).
It's gotta be entertaining, competitive, and have a solid marketing effort. All of which costs money (I'm not holding my breath).