Cannot see enough of it but it looks like an NFL jersey. Hard to tell with colour from just this photo but it will be 9ers, Cards or Falcons if it is. I was wanting to identify it then hopefully mock whoever was wearing it.
I don't know owt about NFL but yeah, knowing the guy whose wearing it, it likely is. I'll ask him on the 24th when I see him see if he can recall. I know he played American football at uni so might explain some of it