If you cut the price on game day, more people will wait to purchase tickets up until then for that reason. You set the price to maximize your profit regardless of the number of seats filled and if you predictably cut your price, you will hurt yourself on earlier sales. You can have 1/2 an empty stadium, but if those people are willing and actually are paying more than double the price of a ticket for a sell out, they will make more money. Marginal revenue = marginal cost to maximize profit. Has nothing to do with having a sellout crowd as odd as that may seem.