It's a shotgun USPSA match. Birdshot and slugs on steel targets and paper. Some stages may have clays (treated as disappearing targets).
I was all amped up to go to my first Harvard match in months but just realized it's not a pistol match this month. I'm actually picking up the shotgun that I'll be converting into my 3-gun shotgun today and was thinking about bringing it, although flying with a shotgun is much more of a pain in the ass than flying with a handgun.