It was an amusing gotcha question, considering Keaton famously played Batman and Ruffalo is the big screen's most famous Hulk.
Playing along, Keaton said, "Everyone needs to stop asking the question of who could beat up who. Batman kicks everybody's a--. And if they won't, I will — Bruce Wayne will."
Journalists, consider yourselves warned.
"Spotlight," which covers the Catholic Church sex-abuse scandal in Boston, is in theaters now in limited release, expanding nationwide at Thanksgiving.