Trent Alexander-Arnold appeared to get away with a clear hand ball on the line to deny Newcastle a goal.
Liverpool full back Alexander-Arnold blocked Saloman Rondon's goal bound effort after it had whizzed past Alisson.
But replays showed that the England international had kept the ball out of the net with his elbow.
If the referee had spotted it, Alexander-Arnold would have expected to have been sent off and the Magpies awarded a penalty.
But fans were left baffled as to why the right-back appeared to get away with it.
One of the suggestions that he wasn't dismissed was that Christian Atsu smashed in the rebound to equalise for the hosts.
Social media was awash with fury over the decision.
Andy wrote: "Trent Alexander-Arnold is a VERY lucky boy As blatant a red card as you’re going to see."
Before he added: "In my humbly biased opinion the ref should have let the goal stand and sent Trent Alexander-Arnold off anyway for blatant cheating."
A City fan said: "Why didn’t the referee sent off Trent Alexander-Arnold?"
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Rayane tweeted: "Trent Alexander-Arnold shouldn’t have been on the pitch but okay.
Olsen added: "Alexander-Arnold with an assist just a few minutes after he should've been sent off for handball... Premier League the only league this could happen"
Virgil van Dijk had earlier handed the Reds the lead in the 13th minute with a free header from Alexander-Arnold's corner.
Liverpool reclaimed the lead soon after when Mo Salah netted his 100th professional league goal, with Alexander-Arnold grabbing a second assist of the match after his controversial moment.
