I was also there. USU declared it "national tequila day."
The atmosphere was unreal. The Cougars took a big lead, but USU did not give up. Then the incident happened. After that, LaVell sent McMahon back onto the field and BYU scored a quick touchdown to put the game back out of reach. I can still remember how McMahon trotted onto the field. He looked totally in control and and had a swagger that exuded leadership. I told the USU fans sitting around me and giving me grief that they were in trouble now. And they were.