the punch

And out of nowhere the fist collided with the face.

Out of nowhere. Out of left field. What do these things mean? And is a punch usually unexpected? Isn't a punch generally preceded by an incident?

But this punch was different. This punch was out of left field. Both literally and figuratively as the fist-owner was indeed sitting on his left, and the punch was wholly unexpected. He turned in expectation of an unexpected argument. The girl grinned. "Merely a love tap," she said and returned her attention to her drink.

He rubbed his jaw in confusion. The evening progressed into night. He kept his eyes on her. She kept her hand in a fist.