Virtually all the standalone antweight events are run like that and it's, in my view, a lot more fun for it - spectators are of course perfectly welcome but they risk having a transmitter shoved in their hands if someone gets two of their own robots drawn against each other :P

The logistics of ants are far different though, the arena(s) can be transported in the back of someone's car and put together in 20 minutes so there's no real costs to recoup by having an audience - which there are with the larger arenas and all that comes with them.