Monday Night Football isn't usually until later in the evening. We were there for the first MNF game (preseason), and it didn't start getting crowded until after 7 for an 8pm kickoff. There seemed to be more people there to catch baseball games than football, though, including a table of about 10 all decked out in Red Sox gear and us in our Tigers caps.
There is no Monday Night Football on Labor Day. On the 10th, there is a 7pm and 10pm game. Aside from that, Monday night games are at 8:30, so I doubt you'd find heavy football crowds as early as 6:30.