Five minutes after Fulham took the lead through captain Tom Cairney, the spotlight was on referee Anthony Taylor.
Fredericks lost possession to Grealish by the touch-line and reacted by appearing to deliberately stamp on his opposing number as he tried to get the ball back.
The incident took place right under the nose of Villa manager Steve Bruce, who was understandably furious when Taylor opted not to take any action.
Fredericks wasn't even shown a yellow card so could now face retrospective punishment from the English Football League's disciplinary body.
Former Villa player Lee Hendrie was analysing the final for 'Sky Sports' and was similarly incensed by the decision.
He said: "The more it is slowed down, the more it is a red card. It is as simple as that and it is right in front of the fourth official on the by-line and something has got to be done there surely. He has got away with absolute murder".