Williams appeared to be disorientated and stumbled after making a tackle early in the All Blacks' 54-34 Rugby Championship win but was not checked by his team's medical staff or the independent Head Injury Assessment (HIA) doctor.
Governing body SANZAAR reviewed video footage of the incident and said that the centre had experienced ataxia -- the loss of control of body movements -- and should have been removed immediately from the field of play.
"SANZAAR has now completed its review of the incident and ... there has not been a deliberate failure or an 'Untoward Incident' ... and as such finds no actions that constitute misconduct," it said in a statement.
SANZAAR, however, added that the incident should have been identified during the match and had contacted all four teams in the competition to remind them of their responsibilities under World Rugby regulations.
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"This is an unfortunate set of circumstances given the acute focus and attention we are all applying to player safety and in particular the HIA protocols," SANZAAR Chief Executive Andy Marinos said.
"As a consequence, and even though there was no deliberate failure apparent, SANZAAR has taken the opportunity to strongly reinforce World Rugby HIA protocols including video analysis during the game, to all teams, match day medical staff and match officials participating in the Rugby Championship."
Williams was cleared of any concussion symptoms after the game and while he was given just a light training load earlier this week, was included in the All Blacks side for their second game against the Wallabies in Dunedin on Saturday.
(Reporting by Greg Stutchbury; Editing by Peter Rutherford)
