I actually have a good bit of experience with an issue like this. To make a long story short, the ACLU and a student club I was in were part of a similar protest of a graduation prayer back when I was in high school. In short: yes, there might be something here, but I think this kind of thing has only really dealt with in public high schools. There seems to be kind of a disconnect between a school run directly by the government and a university receiving public grants and funds. Even if there was an Establishment clause violation, football games are not really a mandatory sanctioned school activity, and as such, this is probably a violation only in the technical sense. But we can leave that to lawyers and constitutional scholars. As an atheist, I really don't give a damn. On a side note, I actually preferred the Lord's Prayer over some of the other, preacher invocations.