They were going to play, but Banner Pilot just issued this statement:
As we said a few days ago, what Ben did at SXSW was lame and unjustified. Other bands and people have defended the punch as justified, a view that we consider to be, uh, insane. You don’t punch someone who spits on you, period. But given that by all accounts it was the first time he had punched someone, and he apologized, we felt it made sense to honor the single show we had agreed to months earlier. A lot of other people seem to equate his punch to a guy beating his girlfriend (ala Chris Brown) or something; we viewed it more as a really, really stupid spur of the moment reaction. Dumb, not justified, but not the kind of thing that would make a person have no chance at redemption. So, it was a weird thing to be caught in the middle of, it wasn’t an easy choice, and we understood the other bands who dropped off. We just decided that, based on everything we knew, we’d honor our commitment to play the festival.
Since then, though, the rest of Screeching Weasel has quit, more bands have dropped off, and no one knows if it will even happen. It’s in a weird limbo. If it doesn’t happen, we don’t want to find out so late that it becomes a pain to adjust our tour / travel plans. And if it does happen, it sounds like it will no longer resemble the show we committed to play.
In other words, it’s a pretty weird situation, and we’re going to bow out of it and will look at setting up a different show for Chicago some other time. Apologies to anyone who wanted to see us at the show. We’ll make it up, promise."