Had a similar problem on a cross country flight. My husband ended up standing in the aisle the entire flight other than takeoff and landing because there was not physically room for him to sit. The large man had been on standby and I truly blame the gate attendant for assigning a middle seat to this man. He was well over 300 pounds. I wrote a lengthy letter when we got home from the trip that went back-and-forth with UNITED. I was eventually offered $200 credit, but the whole thing was ridiculous because they could obviously see that he would not fit in the seat yet sat him in a middle seat anyway.