The punishment, handed down Monday, means Mumm will miss the opening game of their northern hemisphere tour.
The punishment, handed down Monday, means Mumm will miss the opening game of their northern hemisphere tour against Wales in Cardiff on November 5.
Cheika, who launched into an extraordinary outburst after their 37-10 defeat about a perceived lack of respect by the All Blacks, defended Mumm before the hearing, saying Retallick was not an innocent bystander.
"He (Mumm) is trying to get back from being held illegally," said Cheika who refused to congratulate the All Blacks after the game for posting a world record 18th consecutive win.
The blow to Retallick was missed by match officials at the time and judicial officer Robert Selzner accepted Mumm had acted instinctively.
"His opponent was behind him when he tried to extricate himself from his opponent's grip and in that process struck his opponent in the face with his elbow," Selzner said.
"The injury, which his opponent suffered as a result of the incident, did not prevent his opponent from playing on at the time of the incident."
Retallick was diagnosed with concussion at the end of the Test but it was not known if that was a result of the Mumm blow.