Australian Caleb Ewan was disqualified and race leader Kiwi Patrick Bevin was hospitalised as the Tour Down Under erupted in controversy and drama.
Ewan won the fifth stage from Unley to Strathalbyn, but the race jury soon relegated him from first place for a head-butting incident in a chaotic last kilometre.
The official ruling was that Ewan was relegated to last place in the front group for an irregular sprint. Ewan was also fined 500 Swiss francs.
His Lotto-Soudal team manager Mario Aerts said the decision was unfair.
The 149.5km stage went to Belgian Jasper Philipsen, who crossed the line second.
Overhead TV footage showed Ewan appearing to try to head-butt Philipsen as they jostled for position inside the last kilometre.
Ewan was relegated after Philipsen's UAE team, whose sports director is Australian Neil Stephens, approached the race jury.
"Of course, it's unfair to me," Aerts said.
"Caleb protects (himself), to not go in the barriers.
"Then he uses his head - he says 'I cannot use my hands, so what do I do to stay (upright)?'.
"Of course, head butts look spectacular, if they can't use their hands, they have to use something else of their body.
"It's a heavy decision for a light thing to do."
Aerts added Lotto-Soudal were given no say before the race jury made the decision to relegate Ewan, who stays in the Tour.
Ewan did not comment, while Philpsen said he was trying to hold his position.
"I think he hit me twice with his head ... for me it went so fast it was hard to see if it was wrong or not," Philipsen said.
Aerts said he suspects Stephens made the appeal that led to the relegation, but added it was only a hunch.
Ewan originally was ecstatic as he crossed the line.
He has had a tumultuous week in his first WorldTour race with the Lotto-Soudal team, following his split last year from the Australian Mitchelton-Scott squad.
Last Sunday, Ewan won the Down Under Classic warmup event.
Then he was caught out of position in stage one of the Tour, before finishing second in stage two.
Also at today'ss finish, Bevin was in agony and holding his right side after he was caught in a crash 10km from the finish.
Bevin bravely chased back with help from fellow CCC Team riders and rejoined the peloton near the finish.
But he was also bleeding from wounds on his right knee and right elbow and was taken away by ambulance.
"He's a brave and gutsy guy - he went down hard," TV commentator Stuart O'Grady said of Bevin.
The New Zealander ended stage five maintaining his seven-second lead over South African Daryl Impey (Mitchelton-Scott), the defending champion, after they shared Saturday's two intermediate sprints.
Australian star Richie Porte is among a group of climbers who will decide tomorrow's last stage at Willunga.
They are 26 seconds behind Bevin overall and 19 seconds behind Impey