Here's the Chicago Tribune, citing Assistant State's Attorney Barry Quinn:

A group of people had been walking in front of the driver around 11:50 p.m. in the 2900 block of North Milwaukee Avenue when Everardo Custodio, 22, began firing into the crowd, Quinn said.
The driver pulled out a handgun and fired six shots at Custodio, hitting him several times, according to court records. Responding officers found Custodio lying on the ground, bleeding, Quinn said. No other injuries were reported.

The driver had a concealed-carry permit and acted in the defense of himself and others, Assistant State's Attorney Barry Quinn said in court Sunday.

Chicago was home to some of the most draconian gun laws in the US until a 2010 Supreme Court ruling, McDonald v. Chicago, found Chicago's gun-regulation regime unconstitutional.