New Zealand hooker Andrew Hore has been banned for five weeks for striking Wales lock Bradley Davies off the ball during the All Blacks' win in Cardiff.
The suspension means the 34-year-old will miss the All Blacks' final autumn Test against England on Saturday.
He would have faced an eight-week ban for a 'top end' entry level offence.
But it was reduced by three weeks for his "acceptance of guilt, genuine remorse, exemplary disciplinary record and his conduct during the hearing".
The International Rugby Board's Judicial Officer appointed to the case, Professor Lorne Crerar of Scotland, said evidence of Hore's remorse was "his daily contact with the injured player".
Davies was taken to hospital with concussion after the incident, which happened barely 30 seconds into New Zealand's 33-10 win. He will miss Wales' Test against Australia on Saturday as a result.
Hore, who has the right of appeal, lashed out at the retreating Davies, running across his path, as the hooker charged in to clear out a ruck.
Referee Craig Joubert and his two assistants missed the incident, but Hore was later cited.
"The Judicial Officer held that the act of foul play was inherently dangerous, being a deliberate swinging of the arm, delivered with significant force, causing serious injury to the victim player, Bradley Davies, who was unsighted," said a Six Nations disciplinary statement.
"However, the Judicial Officer found that the player had not intended to make contact with the victim player's head."
With Saturday New Zealand's last match of the year, Hore's ban will run until Sunday, 24 February, to take into account his Super 15 province the Highlanders' first three pre-season matches.
"The Judicial Officer heard submissions in detail as to when the suspension should end given that the player was entering the close season," the statement added.
"The Judicial Officer received unreserved assurances from Ian Foster, Assistant Coach, New Zealand, the player and his legal representative that the pre-season matches to be played by the Highlanders during the weekends of 1, 8 and 15 February all had significant and meaningful consequences for the player in accordance with IRB Regulation 17."
The IRB's recommended sanction for striking a player starts at two weeks, with five the mid range and eight or more the most severe punishment.