Years ago competitors had to qualify in a previous contest in order to ender an event on the next level.
But it appears that there was no qualifying event for this contest, so it was most likely an Open Contest with possible lawsuit implications if an individual was denied to to compete.
Back before the NPC existed there was a contest held at the Embassy Auditorium in which one contestant was physically escorted off stage due to his bad physical condition.
And if backstage 'escorts' were not available, the audience would "boo" less than worthy competitors out of the auditorium after assaulting him with rotten tomatoes and eggs.
But I've only seen that happen once.