Room Blocks

A lot of hotels will do a complimentary room block at a set rate for a limited number of rooms. Rooms that are not booked you will not have to pay for. HOWEVER, there are hotels where if you block off a set of rooms, you will be liable to pay for the empty ones. I will caution having your wedding on the same weekend and place of the superbowl. Prices will be outrageous (if you can even get a room block) and I can't imagine travel will be any better.

Some hotel blocks are free, they will hold a certain number of rooms for a set price until a certain cut off date (normally about a month before the wedding)

Some hotel blocks make you reserve a certain number of rooms and you have to pay for any that don't get booked with your wedding

with that being said, if there is a major event MANY hotels will not do room blocks for that weekend because they can make more money by not offering them, OR they wont be at any kind of discounted price. If I were you I would reconsider your wedding date or location unless everyone invited is local.