It was Buzz Aldrin...you can find it on YouTube. The guy deserved it!

Strictly speaking, Aldrin punched the lunatic because he wouldn't stop harassing him in the street, even though multiple people tried to intervene. I can't imagine Aldrin cared too much about the guy's conspiracy theories.

Perhaps in contrast, First Man (the book) relates that Armstrong hid in a college bathroom when some autograph seekers came by the college where he taught.

That was Aldrin.