I watched a guy beat another man on the subway yesterday. After we pulled into the 4th ave and 9th street station on the F train the doors opened and everyone in the car heard a loud smack. A black guy was beating an older businessman with an umbrella. Everyone on the train started making a commotion. "Stop that!" some woman (who had a lot to say even after we left the station) screamed after each hit. Everyone stared at the beating and I think s…