Manager Mikel Arteta fumed after the game that both teams were not at a disadvantage. Hackett agrees and believes the incident was indicative of how the refereeing standards have dropped in recent years.
"That was a very clear and deliberate act, in my opinion he knew what he was doing.
"I was absolutely gobsmacked that VAR didn't intervene, my phone started buzzing after that. I had Mark Halsey on the phone saying: 'How can that not be a red card?'.
"I just couldn't believe it, he's had a look at where the player is and he's whacked him with his boot!
"I'm getting inundated with emails asking why is the standard of refereeing in England declining so badly, let me tell you this: it's through lack of leadership and lack of firm management.
"You can quote me on this, the PGMOL is being run like Butlin's holiday camp!"