Yes, he was. And it's worth reading what he said about managing fear on the football field.
“Let me explain how I feel about fear,” Butkus wrote. “For one thing, we all have it. If you don’t, you’re an idiot. In fact, every player who has ever put on a jersey and pads has experienced fear. The trick is to feel the fear and rise above it. The only way I know to do that is to get good and mad. The anger defeats the fear every time. This technique is as old as warfare itself. From the Romans to the Native Americans to the U.S. Marine Corps, the battle cry remains the primary method of pushing the fear down so far the whimpering can’t be heard. On the football field, there was no one louder than me.”