Everton midfielder Idrissa Gueye was sent off for striking team-mate Michael Keane at the start of the Toffees' game with Manchester United on Monday Night Football.
After Bruno Fernandes' shot flew wide, Gueye - who misplaced a loose pass towards Keane in the penalty area to give the ball away in the build-up - began berating his team-mate.
Replays showed Gueye raising his hand to Keane's face - before being sent off for violent conduct by referee Tony Harrington.
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However, the ferocity of the 'slap' was questioned by Gary Neville on co-commentary.
"How much venom was in that slap?" said Neville. "He has been sent off for that. Was it a little slap or a proper whack?
"There is no doubt a hand comes out to the face but it didn't look too much. They might have had to send him off purely because there is a strike to the face.
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"They were not fighting, it wasn't a scrap. It could have been dealt with by a yellow. I don't think it needed to be a red."
According to the Premier League rules, striking an opponent or any other person on the head or face with their hand or arm represents violent conduct, unless the force used was negligible.
"Was it negligble?" pondered Neville. "That's the question. I think it was negligble. I don't think there was much in that at all."
Gueye becomes the first Premier League player sent off for striking his own team-mate since Ricardo Fuller for Stoke City against West Ham in 2008.
IN PICTURES: Gueye's moment of madness!
Gueye was pushed down the tunnel by Ndiaye
Image: Gueye was pushed down the tunnel by Ndiaye
Pickford had to separate Gueye
Image: Pickford had to separate Gueye
Gueye was moved away from the situation by Ndiaye
Image: Gueye was moved away from the situation by Ndiaye
Everton's Idrissa Gueye is held back after a confrontation with team mate Michael Keane, leading to a red card
Image: Gueye was held back by Iliman Ndiaye and Jordan Pickford
Idrissa Gueye was sent off for striking team-mate Micheal Keane
Image: Idrissa Gueye was sent off for striking team-mate Micheal Keane