It’s Harold Lloyd, in Safety Last!
The scene where Harold Lloyd has to climb up the outside of a skyscraper to escape from a policeman, and he’s just about to climb safely in through a window, when someone opens the window, and he has to cling to the minute hand of the nearby clock to avoid being knocked down into the street.
Don’t worry. That street really was the real background, but Harold Lloyd was being filmed on a nearby rooftop, so if he did fall, he didn’t have far to go. Oops, sorry if I’ve spoilt that for you.
You’re allowed to watch the whole film, if you want, because it’s out of copyright.