Rosenbaum had his hand(s) on Kyle's gun barrel after charging at him. Kyle was fearful of Rosenbaum taking his gun and turning it on Kyle and the crowd. There was no time for 'warning shots' especially as Kyle had just heard Ziminski fire the FIRST shot two seconds before Kyle fired. Regarding Kyle's other two attackers, Kyle was on the ground prone and being beaten on the head/neck with a skate board. The right blow could have killed Kyle or rendered him unconscious. He had NO time to fire warning shot. Kyle's last assailant was pointing his handgun directly at Kyle nearly at point blank range. It was shot or be killed. The jury will scoff at any suggestion that 'warning shots were not fired'.
*and after hearing a clearly disturbed Rosenbaum threaten to kill TWICE.
It's called 'brandishing' and is a felony. Redskin Safety Sean Taylor had been convicted of brandishing which resulted in being barred from owning firearms which led to his death as he was unable to defend himself, his wife and baby during a subsequent armed home invasion.