The injured man was the fourth to land and hit the pitch after coming in too fast, his leg buckling on impact.
He appeared to yell in agony as he lay prone on the Eden Park turf for several minutes before St John Ambulance staff attended to his leg injury.
Witness Marvin Appricot said he had never seen anything so nerve-racking in his life.
"I thought someone was going to die, or hit the goal post, or hit the edge of the roof.
"It was awesome."
Another witness said it appeared the first skydiver came in too low, hit the ground hard and was lucky not to injure himself.
"[The] tandem jump landed fine, but the next four jumpers were all in trouble, and the guy who injured his leg could easily have broken his neck, he hit very hard.
"One almost took out the announcer/cameramen in the middle of the pitch, and it wasn't staged ... it was quite disturbing," the man said.
Tua Numanga, last year's Vodafone superfan, was on the field when the six parachutes started "dropping like stones" once they passed the top of the stadium.
"We heard a big crack when he hit the ground. We had to jump out of the way because we didn't realise they were coming in all over the place," he said.
"We were looking at this person coming at us and thought, 'Geez, we'd better move'.
"The skydivers didn't look like they were panicking though."
Skydive Auckland director Tony Green said they were contracted to bring in the Superfan winner.
The injured man was not one of their employees but was associated with the company.
Mr Green said the man, who he believed was in his 40s, called him from his bed at Auckland City Hospital to say he was "doing fine".
"I don't think it's as serious as everyone first thought."
A hospital spokeswoman said the man underwent a procedure on his leg last night but was in a stable condition.
Mr Green said the man was very experienced and had been skydiving for about 20 years.
He said it was "extremely tricky" landing in stadiums because the winds were hard to navigate and were typically "quite swirly".
They had been planning and organising yesterday's jump for several weeks, Mr Green said.
"He had been asked to do the tandem jump with the Superfan and then some of the other divers wanted to come along as well."
The Warriors' general manager, Don Mann, said they were hoping to catch up with the injured man today to work out what went wrong and to see how he was doing.
He said the Superfan's landing went smoothly and the man "thoroughly enjoyed" himself.
