The Writer Thomas Gibson Kicked is An Aggressive Badass

The writer Thomas Gibson kicked on the "Criminal Minds" set is anything but a nerd ... he's a boxer/martial artist with a super aggressive attitude -- sources connected to Gibson tell TMZ.

Virgil Williams is the writer/co-executive producer who got into it with Gibson when the argument escalated to the point the actor kicked him. But our Gibson sources say Williams escalated the verbal argument by "making a move" toward Gibson in a highly aggressive manner. They say Gibson's kick was more a reaction to the perceived threat than an aggressive move.

Our sources say Williams lets everyone on the set know ... he's trained as a boxer and does martial arts.