A person who stabbed a man in the back after a fight aboard a CTA bus in Greater Grand Crossing was in custody Friday. About 9:35 p.m. Thursday, the victim, a 35-year-old man, was on the bus in the first block of West 79th Street when he got into an argument with someone that turned physical, Chicago police said. At that point, the two exited the bus, and the suspect pulled a knife and stabbed the 35-year-old in the back. Responding officers placed the attacker into custody while the victim was taken by paramedics to the University of Chicago Medical Center in good condition. No charges have been announced.