Fans watching the game posted video of the scene, shortly after the incident, to YouTube:
According to police, the 45-year-old ref was knocked unconscious during a World Class Players Cup match at the Credit Union Eventplex.
People at the match, between Sudan and Poland, said it was a player with the Sudan team who threw the punch.
"Preliminary investigation indicates the victim had been struck in the jaw, causing him to fall, unconscious, to the ground," the Regina Police Service said in a press release.
Hussam Ibrahim, who's from Sudan and was watching the game, which Poland won 4-1, said emotions were running high.
"Things got out of hand, people started fouling and tackling each other," Ibrahim said.
The referees handed out two red cards to Sudan and two red cards to Poland.
According to a statement from the WCP, there was a brief scuffle on the field when those red cards were issued and the situation flared up when another red card was issued a few minutes later.
"All hell broke loose," when the ref went to deliver a third red card, Ibrahim said.
"I didn't see a punch, but he touched his [the ref's] face," Ibrahim said. "By no means am I justifying it, no touching should ever happen ... but from a fan's point of view, the ref overreacted."
The referee refused an ambulance but was advised to seek medical follow-up, police said.
Police were on the scene and searched the locker room and other areas of the building, but couldn't find the suspect.
According to the WCP, after the incident between the player and the referee, the game was declared ended and everyone left the field.
The organizers then called the police.
"The WCP Cup Organizing Committee takes the position that the striking by a player of an official is outside of the scope of the game and as such, the local authorities were contacted," the committee said in a news release.
Police haven't released the suspect's name, but said it's believed he's from Alberta.
The incident has attracted attention on various social media platforms, including Facebook where Anthony Banerjee posted a video to his account that provided a sense of the heated atmosphere of the soccer match. The video shows another part of the game, not connected to the alleged punch, where players were involved in a scuffle on the field.
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