Officers said the policeman was on duty at a Edmonton Eskimos game before a auto rammed into a police vehicle.
An Edmonton Police Service officer was working traffic control behind a barricade. The officer was outside his vehicle, which had its lights flashing to improve visibility.
A driver of a Malibu Chevrolet crashed through traffic barricades at 8.15pm.
The impact sent the officer flying at least 15 feet into the air, he said.
Police arrested the suspect and said they had "no forewarning" of the attack.
The driver then gets out and appears to stab the officer, who wrestles the suspect to the ground and then rises as the suspect flees on foot.
Knecht said details on the identity of the registered owner of the vehicle were distributed to officers. The driver took off again, prompting officers to give chase to the large U-Haul van. Four were taken to hospital. Their conditions were not immediately known, the police chief said.
Witnesses who saw the chase and pedestrians being struck described the scene as chaotic.
One local bar manager told The Globe and Mail that he had seen the U-Haul come careening down an alleyway next to his establishment, striking two patrons.
It "peeled" into an alley where people were smoking, he said.
"It seems to have been carried out very badly (thankfully) so probably not a mastermind here, folks", she said on Twitter.
The U-Haul ended up on its side a few blocks away outside the Matrix hotel. "We have to show that's not going to happen, not in Edmonton", said group spokesman Aurangzeb Qureshi. "This is a lone individual", he said.
A high-speed chase followed where the suspect deliberately tried to run over pedestrians.
"Holy shit, this is too fast", he thought as he watched vehicles driving west on Jasper Avenue. Knetch said the high-speed pursuit in the downtown area was justified by the serious nature of the incident. Then he says he heard what he believed was a gunshot.
A suspect, aged around 30, has been arrested and the authorities believe he acted alone.
Goodale added that the investigation into the incident is still in the early stages. Police officers put themselves at great personal risk every single day on our behalf, and this attack is a stark reminder of the sacrifices they make for the public good.