Last Braves game I went to, they were checking bags at the gate. I emptied my backpack and stuffed all my junk in my pockets to help things along.
After looking all through the empty bag, the guard started to hand it back, then noted to two straps and said "Wait, this is a backpack, you can't bring it in here."

The lady in the next line with the 18 cubic foot, filled to the brim diaper bag went right on in.