I watched the video several times. The 75-year-old man at one point reached and touched the police officers‘s gun or gun belt. The officer looked surprised, and as a reaction shoved the man back. The man kind of tripped over his own feet. I put this 90% on the 75-year-old man and 10% on the police officer. Obviously, the officer didn’t intend to hurt this guy. He certainly doesn’t deserve to be fired.
I agree...doesn't even look like the cop pushed him hard at all. I'd say the civilian tried to make it look like he was pushed hard and ended up tripping.