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.Ultimately, the pap decided not to press charges ... maybe because he knew just how much he had baited LeNoble.  Christina Applegate's rock star husband was detained by police in Studio City yesterday after allegedly roughing up a photog ... but the Porno for Pyros bassist insists the pap crossed the line by taking photos of his child. The video begins with rocker Martyn LeNoble being approached by police on a street corner in broad daylight -- he was detained, and patted down. LeNoble -- who was not handcuffed and not arrested -- then begins to tell his side of the story ... insisting a paparazzo (not a TMZ guy) tried shooting photos of his wife and 2-year-old daughter at a birthday party. LeNoble says, "I went outside to talk to him and he got physical with me ... he wouldn't back off."At one point, LeNoble says the pap challenged him to a fight in a back alley -- saying, "Let's see what kind of man you are."Eventually, LeNoble was released and sent on his way without further incident ... though it sounds like he may try to take legal action against the snapper. Celebs are clearly drawing a line in the sand about kids and it's creating a lot of issues, because there are some photographers that are not backing down. As far as the pap is concerned, law enforcement tells us the guy isn't pressing charges.  A creepy Twitter fan is threatening Christina Applegate and her fiance with terrifying messages like ... I'll "blow your f**king head off!!!" -- and LAPD has launched an investigation, TMZ has learned.Law enforcement sources tell us Applegate's fiance, musician Martyn LeNoble, got the threatening tweets on Sept. 20th -- and according to documents filed in the case, they included: "You stole [Christina] away from me. If not for you she would be mine."The tweet continues ... "I will not accept this. I am going to kill you!!!!!!!!!"LAPD obtained a search warrant 6 days later -- which was served on Twitter HQ in San Fran -- and the docs list several other violent threats:- "I'm going to bust your head in for taking her away from me!!! Be afraid, be very afraid!!"- "You think this is a joke? I want to see how funny you think I am when I blow your f**king head off!!!"The big problem cops are facing is ... Twitter is so damn anonymous.According to the search warrant, LeNoble didn't recognize the Twitter profile sending the threats. Police want to access Twitter's records related to the profile ... which has been deleted. Applegate's rep hasn't returned our call for comment.
Martyn LeNoble on TMZ, your go-to source for celebrity news, photos, & videos. Latest Story: Christina Applegate's Husband -- Photographer's Footage Shows the Angry Face-Off