The water in the pool was about one metre deep.
"He went a bit too far and just kind of hit the side [of the pool] . . . it was pretty tragic," one said.
"It's been rough, but we are just holding up for him."
According to ENSOC's guidelines for potential candidates, nominees were supposed to tell the AGM adjudicator what their stunt would be prior to filming it.
Stunts likely to hurt the candidate or anyone else would not be accepted, Fairfax reported.
University of Canterbury vice-chancellor Rod Carr told the Herald in a statement a student had been injured at a private residence last week.
"The University has met with the student's family to offer its support.
"The student's family has requested privacy and the University will be making no further comment."
ENSOC did not wish to comment on the incident, he said, adding that the university worked with the students association to ensure students and clubs acted responsibly.
Police were aware of the incident and would be making inquiries.