I missed this when I saw The Winter Soldier. Natasha grabs Steve and pulls him away from one stream of bullets and then proceeds to shove Sam out of the way of more bullets with her foot. <<< Yet another demonstration of Black Widow's awesomeness.
She does know from experience. He trained her in the Red Room. He doesn't remember her, and we've seen no evidence in the MCU that she remembers him from the Red Room, but these two DO know each other.
Which MCU character are you? < I got I got Captain America - You’re a bit uptight and by-the-book, but your old-school values serve you well for the most part. You are an extremely decent person, and would do anything it takes to help people in need.....explains why I am #TeamCap in civil war and why I am so #TeamBucky!! ♥♥