Call me crazy, but I’m sure the Grifball map rotation doesn’t contain Underpass. Been playing for hours and it’s still not turned up. Granted, i haven’t played Frontier either, but I’ve been asking around my friends and Spartan company, and nobody seems to have seen it. Same goes for all the YouTube videos related to the update - nobody has video footage of it being in the playlist.
I played about maybe 20 games of grifball yesterday and never got it.