Ticketmaster owns the contracts to every major venue.
Great... there's a hell of a lot of smaller venues, festivals, and other events that can be taken whilst Ticketmaster ignores you and you add significant value. By the time you worry about Ticketmaster or they worry about you, you already have momentum from artists, promoters and fans, and due to the bad press Ticketmaster gets through their tout-resell sites you also have political pressure.
Ticketmaster is built in to this plan. Their presence makes the grassroots stuff even more compelling as you don't have to boil the ocean, you figure out how to make it work on a small venue level, city level, and go for scale in the bottom layers.
Worst comes to worst, they're forced to consider purchasing you as you take all of the oxygen out of the system that feeds artists and promoters into them.