Joey Gazelle (Paul Walker) is a low level mob flanker. During a deal his boss Tommy (Johnny Messner) masked men burst in and try to steal the drugs and money. The stand-off descends into a shoot-out and several of the masked men are killed before the leader flees. Joey discovers a badge on one of the dead men, revealing that they were dirty cops. As the mobsters flee in a panic, Tommy gives the murder weapon to Joey, telling him to get rid of them. Joey comes home to his wife Teresa (Vera Farmiga) and son Nicky (Alex Neuberger). He hides the gun in the basement while Nicky and his best friend from next door, Oleg (Cameron Bright), secretly watch. At dinner time Oleg returns home to his battered mother Mila and his abusive stepfather, Anzor Yugorsky (Karel Roden) the nephew of a psychotic Russian mob boss Ivan (John Noble) ... who happens to be in business with Joey's crew on a gasoline scam.

When Anzor beats Oleg’s mother Mila (Ivana Milicevic), he steals the weapon from the basement and shoots Anzor. Next door, the Gazelle family is disrupted by the gunshots and Joey rushes next door. He finds Anzor wounded but alive, and discovers from him that Oleg has fled with the cop-killer gun. Now Joey has to find the kid and the gun before the police and the mob find them first. Oleg, in turn, wanders through a sinister urban landscape and encounters a series of often nightmarish characters. He initially runs afoul of a hobo who attempts to use the gun to steal a drug stash. After the hobo is killed, while running around a the corner of a small building, Oleg abruptly runs into a female prostitute being abused by a pimp. Oleg help the woman with the pimp and when he undergoes an asthma attack, the prostitute takes him to the nearest pharmacy to get him an inhaler. Afterward, the prostitute takes Oleg to a nearby diner to get him a hamburger.

Joey takes Nicky with him to find Oleg, but before he meet his mafia associates at the same diner, but only Nicky notices Oleg. Nicky sneaks away and meets with Oleg in the diner bathroom, where they hide the gun in a toilet. Meanwhile, the mobsters confront Joey on the status of the missing gun. Detective Rydell (Chazz Palminteri), the leader of the dirty cops, has connected the gun that shot the dirty cop with the gun that shot Anzor. As Joey drives away, Nicky admits that he met with Oleg and stashed the gun, but the gun is gone by the time Joey returns to the diner.

Meanwhile, after a painful reunion with Anzor and refusal to let him know where the gun is, Oleg escapes the ice cream parlor they are at into the parking lot, sneaking behind parked cars as Anzor storms out after him, ultimately unable to find him. Climbing into the back of a van, Oleg accidentally falls into the clutches of an overly-friendly, married couple Dez and Edele who take him along with two other kids back to their apartment. Oleg quickly realizes that the couple are pedophiles/child sex abusers who have kidnapped him and may kill him at some point in the near future. Using an excuse of an upset stomach to go to the bathroom, Oleg at first sticks a cellphone and calls up Teresa Gazelle to help him. Oleg grabs a prescription medication and tell her the house’s adress.

Teresa  arrives and knocks on the door, Telling that Oleg called her from their apartment, Edele attempts to assure Teresa that she has the incorrect address. Threatening to call and wait for the police to arrive, Edele hesitantly lets her inside. Searching through the entirety of the apartment, Teresa finds no trace of Oleg. Turning his threat back on them both with child abduction, Teresa pulls out a gun from her purse just as Edele advances on her, yelling at them to tell her where Oleg is. While the couple remains silent, Teresa notices something in the nearby closet and opens it to see an unconscious Oleg fall out, his hands tied and a plastic bag wrapped around his head. Oleg revives and Teresa cuts his bindings loose, she instructs Oleg to get the two other children from the bedroom and leave. Teresa finds in the closet behind her shelves of several DVD cases with children's names on them. Teresa calls the police, giving an address to the apartment building and reports hearing gunshots from across the hall. She hangs up and shoots them both dead.

Meanwhile, Joey continues to search for the gun as his mafia associates become violent and the Russian mob gets involved in the affair. All the various criminal factions, along with Oleg and Joey, meet at a hockey rink. The various members trade accusations and alternative theories of the truth as the meeting descends into a shootout. All of the crime lords are killed but not before Joey reveals that he is actually an undercover police officer. Finally, a battered Joey and Oleg emerge. Joey takes Oleg out for some breakfast, but a fellow diner turns out to be the pimp that Oleg had previously encountered. The pimp threatens Oleg with a knife and produces the same gun Joey had previously been trying to locate. In the ensuing struggle Joey kills the pimp by stabbing him in the neck.

All the while, Oleg's mother has locked herself up in the shed behind their house, she holds up a lighter right in a cloud of propane gas escaping from a tank she opened, blowing up the shed and part of the house, killing herself. All the while, Joey soon loses the ability to drive and, barely reaching his house, he passes out from blood loss into Teresa’s arms.

Thomas Jane declined the role of Joey Gazelle due to scheduling conflicts. Paul Walker was a second choice.

The medicine bottle that Oleg uses to find the address of Dez and Adele's apartment is a prescription for Zovirax, a medication used to treat herpes.

Runnig Scared is actually number 7 on the most times F**K is used in a movie list, with 328 times. In this “special” list it came before  the movie Godd Fellas (1990), also starring Chazz Palminteri, with 287 times, about 1 time every 28 seconds. In Runnig Scared  the average is 1 time every 21 seconds. The record for most swearwords belongs to the movie cartoon South Park (1999) with almost 400 rude words.

Most of the bloody gunshot wounds were CGI. The only real squibs used were in the Black Light Hockey Rink Shootout.

Detective Rydell, the character played by Chazz Palminteri, is named after actor/director Mark Rydell, the director of The Cowboys, a film referenced many times in this film.

The 95% of the movie was shoot in Prague, only the 5% in New Jersey. The diner is a real diner in New Jersey, the interios are been re-buil in Prague.

A 2-disc DVD was released in France. The second disc contains all the extras, plus  a gallery, production notes, and 2 exlusive interviews with Paul Walker and Wayne Kramer.

Initially Warner refuses the premission to use a clip of The Cowboys. Wayne Kramer change the screenplay, making Anzor acting under the drug's effect to  justify his behaviour, and have Warner's permission.

Pimp Lester: [pointing gun at Oleg] Say hello to my little friend!
Joey Gazelle: That's real f**kin' original. What are you, a f**kin' cartoon?
Pimp Lester: I'm a Mac Daddy pimp! You know that. And now I'm gonna cap your ass, and when I'm finished with you, I'm gonna take your little punk friend and I'm gonna put him in my posse, and I'm gonna pimp him out for a couple of months and then I'm gonna take that knife of yours and I'm gonna cut him from ear to ear, *just like I should've done yesterday, you f**k!*
Joey Gazelle: Yeah, I'm sure that sounds great to you all in your f**kin' pimp world and all, but listen, right now that's not the f**kin' thing you wanna do! You wanna put down that f**kin' gun, and you wanna walk away 'cause I swear to f**kin' God, I'll f**kin' kill you, you f**kin' pimp b**ch!
Pimp Lester: Wrong! Only one of us is walking out of here. Guess who?
Joey Gazelle: Oleg, get behind me. ... Oleg, get behind me!