I've seen a lot of speculation as to what went on. I am not certain but when I attended as a freshman in 1980 they simply punched our IDs. People often sat 3 in 2 seats worth of space but my recollection is that there was an organized student group protesting the portion of the activity fee that was included in everyone's fees dedicated to athletic events since they did not attend any athletic events at all. The general consensus at the time was the "free" attendance of games was doomed.
I left LSU after that year and finished my college career an hour west of Baton Rouge, permanently ruined for any other college football experience. I only attended 1 game at my alma matter as a student, it just didn't measure up, I did manage to go to a couple of LSU games in that time though.