I was told that Ford was very sick that day and wasn’t up to all the fight scenes so he asked the director “Why can’t I just shoot the guy?” The director said OK and they ended up leaving it in.
Yep, I've read that also. The making of a classic!
I'd heard that Ford forgot what he was supposed to do and ad-libbed it. Regardless, it's still a classic scene and I still chuckle over it whenever the movie's on TV.
Will check out the You Tube stuff tonight, work blocks it now :(