sometimes relievers just end up dead overnight. doo isn't the first or last reliever to show some cracks, rebound, then just fall off completely. he's probably cooked, best case he's a middle of the pen guy.
Which relievers came into a season with dead arm? Dead arm is a fancy way of saying fatigue. That's all. Doolittle has nothing to be fatigued over because he hasnt done anything for 9 months. He threw 17 innings the last two months of the season.
He isnt anything in his current state. He is throwing batting practice. Put him on the IL, let him work out his crap away from the team. But as it stands, he can't locate. He cant throw hard. And hes trying to develop secondary pitches in real games. He isnt a long term piece here in DC, so let him get better and ready for what amounts to a free agency try out.