Reports indicated the native of New Westminster, B.C., exposed part of his buttocks to the crowd at Mosaic Stadium. Stampeders coach and general manager John Hufnagel confirmed Monday that Cornish "pulled his pants down low" during the game.
"The incident was a mistake on my part," Cornish said. "I definitely took things too far and it reflects poorly on the organization. First of all, I want to apologize to coach (Hufnagel), all the coaches, my teammates, all the Stampeders fans and Stampeders organization and to the Riders fans and organization.
"It was an extreme lack of judgment on my part and I apologize to everyone in the CFL and to the commissioner. Nobody deserves to deal with this and I apologize to everyone involved."
Cornish, who leads the league with 947 rushing yards this season, was held to just 67 yards Sunday as Saskatchewan beat Calgary 30-25 to end the Stamps' four-game winning streak.
"I think you see how disappointed Jon is in himself once he fully realized the seriousness of the matter," Hufnagel said. "I'm very disappointed in Jon Cornish. He took things way too far and it needs to be dealt with.
"I've had a chat with Jon about it, he knows my feelings about it, he knows our president Lyle Bauer's feelings about it. He will be disciplined."
Cornish has scored eight touchdowns this season. He also has 24 receptions for 171 yards.
"It's an embarrassing incident that does not reflect the expectations we have for our players," Bauer said in a statement. "We have great pride in the organization and respect for our opponents and their fans.
"I believe that Jon Cornish learned a great lesson in being a true professional today and the proof of that is his willingness to stand up and admit his error publicly."
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