What worried Uncle Hammer about going to Chicago?

Hammer wasn't so much worried about going to Chicago, as he was worried about something happening to his brother.

“No,” said Papa adamantly, “You do better in Chicago.”

“May do better but I worry a lot.” He paused, pulling at his ear. “Come through Strawberry with a fellow from up in Vicksburg. Things seemed worse than usual up there. It gets hot like this and folks get dissatisfied with life, they start looking ’round for somebody to take it out on…. I don’t want it to be you.”