Sure, they had fought before. Dean had even let Sam think he’d really hurt him a time or two when they were younger. But even while Sam grew and surpassed Dean in height, he’d never been able to floor his older brother in a fight. Not once. Until now. In this moment, Dean knows it’s over. His pleading and actions from here on won’t mean anything. Sam’s made up his mind and the blow that sent his brother to the floor was the final seal. So why fight? Why go up against a man with the strength of a demon? Because it’s all he’s got in him. One last fight. One last way to prove to Sam that he’s not just going to give him up to Ruby, to the demons, to fate. Maybe there’s a snowballs chance in hell he can beat some sense into his brother, but it’s far more likely that Sam will beat the life out of Dean. Either way, it doesn’t matter. He’d rather be dead than see Sammy do this to himself.