bad officiating, through the ref not dealing with problems earlier in the game, now he has lost control.
I want Palace to win, but this ref allowed the time wasting to go on for too long, then when he decides to start making decisions, he completely fooks it up.
Booked tomiyasu for a pull back when he was on a yellow but ignored Ayew pull back on Saka when he was on a yellow.
Probably up to about 15 minutes to be added on so far with the pen, subs, bookings, sending off and all the Arsenal time wasting.
I don't think it's even about that, he just didn't stamp his authority on the game, so players thought they could get away with stuff, then he starts brandishing more cards than he needed to due to his own incompetence.