Christina Applegate's Husband -- Photographer's Footage Shows the Angry Face-Off

Christina Applegate's husband was mercilessly hounded by a paparazzo -- and may have gotten annoyed enough to reach out and smack the guy.

As TMZ first reported ... Porno for Pyros bassist Martyn LeNoble was briefly detained by police after a weekend incident where a freelance pap (not one of TMZ's) accused him of getting physical.

LeNoble told cops he was trying to stop the photog from shooting his family during their daughter's birthday party -- when the guy challenged him to a fight in a back alley.

The photog's own video backs that up, as he tells Martyn ... "Let's fight over there. Let's go to the alley. Let's see if you're a man."

Look, the paparazzo is clearly being an antagonistic jerk ... but LeNoble does appear to smack the guy's camera at some point.