'Barton's been compromised.'
Coulson's simple statement, and to the outside observer it would have been as casual of a comment as saying they were serving tomato soup for lunch today, was still echoing in Natasha's mind hours later.
She knew better than to think it was so unemotional of a comment. The almost undetectable edge in Couslon's voice, the hesitation, the worry. The Black Widow picked up all of that, in the voice of the one man she was sure was the most unflappable person in all of SHIELD save Fury. Phil Coulson was worried. Phil Coulson was not sure what was going to happen, or how they should handle a situation. That scared the hell out of her.
She put on the usual hard expression that would keep anyone from bothering her as she made her way down the hall. Yes, she should have been watching Banner and preventing Stark from being...Stark. She should have been making sure poor defrosted Steve wasn't overwhelmed. She should have been doing a lot of things considering there was a crazy god of mischief using her best friend to try and bring the world to it's knees.
But she could spare ten or twenty minutes to go knock a few punching bags around. Natasha wasn't focusing, and that would help no one when it came time to do or die. Especially herself. Hopefully no one with any authority would find her and try and stop her, because she wasn't in much of a mood for 'Yes, sir. No, sir. Thank you, sir." She simply wanted to dispense with the distracting thoughts in her head and get on with her life.