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9:14 AM PT -- Law enforcement sources tell us the police have reviewed the video and have launched a criminal investigation with Katt as the target. Katt, who is also on bail for multiple assault charges, is currently out on bail but one of the conditions is that he keeps his nose clean. The police are also reviewing the bail order to determine if he violated and whether bail should be revoked.

Katt Williams threw a punch at a kid, but when you watch the video it's clear the kid ends up kicking Katt's ass.

Katt throws the first punch but the victim -- who's reportedly in 7th grade -- takes matters into his own hands and puts Katt in a rear naked choke.

Katt was in Gainesville, an hour outside Atlanta handing out cash ... it's unclear how things went south.