Joel Matip and the Liverpool fans lost their cool with referee Paul Tierney on Sunday.
The Reds defender was shown a yellow card for a challenge on Brentford’s Christian Norgaard.
Matip got the ball first but went straight through the Bees player, leaving him in a heap on the ground.
Tierney immediately blew his whistle and showed the card to the defender.
The referee started trending on social media with Liverpool fans fuming with the decision.
It was not all miserable for the home side, though, as they went into half-time 1-0 up.
Darwin Nunez had two goals correctly ruled offside before he then produced an assist for the opener in the 39th minute.
The Uruguay international was centimetres away from being onside for the first, but the second was rightly ruled out by a much clearer margin.
For the goal, Alexander-Arnold picked out Nunez on the edge of the area and he laid off to Mohamed Salah who tucked a shot past Mark Flekken and inside the far post for a goal of brilliant simplicity.
There was a potentially questionable line decision in the 63rd minute as Gakpo’s cross to the far post looked to have gone out before Salah headed home, which was why there were muted celebrations for the Egyptian’s landmark 200th goal in English club football.
However, VAR ruled in favour of the home side and the goal was allowed to stand.
Diogo Jota capped a dominant performance with the third in the 74th minute, cutting in from the left to fire home from the edge of the area.