already in town for a concert or the game in a town that could accommodate a concert right before or after the game for example. A national championship level game might carry the exposure sufficient to make it worth it for Metallica to show up just to play one song to kick off the game (and maybe a couple at 1/2 time). otherwise, they're not travelling, rehearsing and setting up just to play 1/2 of enter sandman at the start of a game. the video board message may be the best we can realistically ever expect to get.