Clint hesitated. As well as he used to know Natasha, he balked at the idea of speaking on her behalf. They'd misinterpreted each other so much, especially lately, and the last thing Clint wanted to do was give Steve the wrong information. But he had to tell Steve something. Much as he wanted to defend Natasha for her own sake, though, he resisted the impulse to tell him that she'd done this for Steve's own sake, that her heart wasn't as hard as he assumed. Natasha herself probably wouldn't agree with that analysis.
So instead, he gave Steve the answer that Clint, deep in his heart of hearts, genuinely believed was the most true. "She wasn't just protecting you, Ace," he said, his voice so soft, but so heavy at the same time. "She was furious when I filled in at your Victor Tour. But she... knows me. She understands how invested I am in you. So I think part of it was because she knew you wouldn't be able to handle it. And part of it was because she knew I wouldn't be able to. Doing it myself, that's one thing. I've been here twenty years; I know how to handle that. But watching a thing like that happen to someone you love while you stand by and do nothing," Clint shook his head. "There's nothing more destructive than that."