Was definitely surprised to see this. So, with all the talk about why he was fired instead of "mutual parting", I was thinking it might've gone down like this: Sark is looking at all areas that need fixing. One of those areas (and not the greatest need) is defense, especially vs Georgia. He finds out Boom is available and interested, which is definitely an upgrade. Calls in PK - who wasn't terrible but has some weaknesses - and tells him he's going to hire Boom as Co-DC with playcalling responsibilities and wants PK to stay as co-DC but step down to position coach, but gives PK the opportunity to voluntarily step down and announce he's leaving for other opportunities, family, health, whatever. But PK isn't interested in being #2 on defense, or isn't willing to walk away quietly, and basically tells Sark (or CDC), "Fuck you. If you want me gone, you'll have to fire me." And so he's been fired. Probably more plausible than anything performance related. Maybe slightly less probable than personality conflict.