The outfit is the result of a mostly friendly game played by during practice by the Cardinals. They try to lob balls into a garbage can and the winners get to choose a game day outfit for the loser. That's how cornerback Patrick Peterson wound up dressed as Buddy the Elf last season.
It's probably not a great sign if your starting quarterback loses that contest, but it worked out ok this week. Palmer had a massive game, throwing for over 300 yards and three touchdowns, leading the Cardinals to a win.
Maybe he should dress as the Stay Puft Marshmallow Man every game. Though, that swishing noise when he walks would drive George Costanza into madness.
Watch Palmer's warmups in the video above.