Referee Craig Joubert's run from the pitch at the end of Scotland's defeat by Australia may have been prompted by crowd "hostility", says World Rugby chief executive Brett Gosper.
Joubert, 37, awarded a controversial penalty that gave the Wallabies a 35-34 win in the quarter-final at Twickenham.
At full-time, he ran from the field without shaking hands with the players.
"When you have a hostile 82,000 people, for whatever reason, who knows how that affects behaviour?" said Gosper.
"I'm sure as a referee he sensed a bit of hostility."
Former Scotland captain Gavin Hastings described Joubert's swift exit from the field as the "the worst thing I have seen on a rugby field in a very long time". Matt Dawson, part of England's World Cup-winning side of 2003, said it was "disrespectful to the game".
"Maybe he was keen to get to the bathroom, who knows?" joked Gosper to BBC Radio 5 live.
"Craig Joubert is a superb referee and has been for a long time and he's a good man. There will be reasons for whatever Craig did.
"We do a full review of the referees post-game, and that process is under way at the moment."
|World Cup semi-finals|
|Saturday, 24 October, 16:00 BST||South Africa v New Zealand||Twickenham|
|Sunday, 25 October, 16:00 GMT||Argentina v Australia||Twickenham|
Scotland led Australia 34-32 with two minutes to go when Joubert ruled Jon Welsh was deliberately offside, awarding a penalty that Bernard Foley kicked to earn the Wallabies a place in the last four.
However, replays suggested Australia's Nick Phipps touched the ball back to Welsh and Joubert could have awarded a scrum rather than a penalty.
Scotland coach Vern Cotter and captain Greig Laidlaw believe Joubert should have consulted the television match official, although tournament regulations only allow the officials to use video replays to rule on foul play, or whether tries and kicks at goal are legitimate.