His stamina looked worse this fight, but that was probably due to a combination of getting mauled and beaten on and carrying around ten pounds of useless steroid muscle. He looked way more dangerous at a lean 215-220 to be honest.
You burn up a lot of nervous energy when you're getting battered and humiliated like that. Both Bootleg D and AJ were in shock after getting dropped by Fat Level fighters like Fury and Ruiz and it dawned on them that it was going pear shaped. Underrate Fat Level fighters at your peril. This wasn't supposed to happen This content is protected
True and that certainly doesn't help matters. But Bootleg D started blowing pretty early in the fight - the KD in round 3 took a lot out of him mentally and I think the fear was sapping his tank gradually from the instance Fury set about him in round one.
Well rumour is that his ringwalk attire was powered by concentration and will like Green Lantern's ring so that prob took a lot out of Deontay mentally if true. I can imagine a sustained thought to be quite the task for him.