Steve stood in front of Bucky and gripped his human shoulder, trying to stop him from moving forward and hurting Tony any more. Sure he restrained himself from attacking him further, but Steve didn't want to take any risk. Bucky was quick and rather unpredictable after all.

"It was probably an accident."

He didn't fault Tony, this technology was new and he probably made a mistake. Those things happened. Steve was certain that he wouldn't hurt Bucky intentionally, especially since the former assassin could hurt him. Which. He did.