User blog comment:RainDance96/RWBY's first murder?!/@comment-3146930-20140725181727

A single kick probably wouldn't kill him unless Mercury had his boots loaded with bullets. Yang's gauntlets seem to use a type of energy blast that can hurt someone, but not kill them. Anyway the kick may have simply knocked him out, then they killed him when he was down. Obviously there was a time skip, as I don't think the RWBY team wanted to show a guy being killed (RWBY is supposed to be a family show), possibly painfully.