Ten Hag said after the 2-1 win at Old Trafford: "The player from Crystal Palace takes a big risk by this foul that he gets badly injured by pushing him across the line and you know the pitches here. And then everyone is reacting, Crystal Palace and Manchester United players, and not only Casemiro.
"He (Ayew) was one of the players who did even worse than Casemiro. Casemiro, you freeze the moment, I think within the shot he's crossing the line there, I do definitely. And you have to be consistent as a VAR.
"Last week we missed Christian Eriksen by a bad foul - no interfering by VAR. Mateta is elbowing Martinez, he is running with two weeks with [a bandage] on his eyebrow and [VAR is] not interfering. So I see this is not right and this is in the game and an influence on the game but also coming games."
Casemiro was dismissed after he grabbed Palace midfielder Will Hughes by the throat. A review by the VAR advised on-pitch official Andre Marriner that Casemiro's action was violent conduct and warranted a straight red card.
During the same melee that spilled off the pitch, Ayew appeared to have his hand around the throat of United midfielder Fred but that was not deemed a red card offence.
Ten Hag also blamed Jeffrey Schlupp for causing the 66th-minute flashpoint when he shoved United winger Antony into the pitchside ditch. Antony retaliated and both players were booked.
