Seth wears a shirt during the basketball game featuring the number 88. This is a Nazi skinhead code for HH, or "Heil Hitler," H being the 8th letter of the alphabet. It also refers to a set of 88 precepts written by the neo-nazi leader David Lane. The 88 precepts are rules and concepts that all White Supremacists lived by.
The diner that Danny and Derek get breakfast before Danny goes to school in the morning is the same diner that is used in The Big Lebowski (1998), during the infamous "toe" scene. The is located at Wilshire and Fairfax in Los Angeles. It's called Johnie's Coffee Shop and is only open for filming.
In the first flashback where Derek has fired at the car and is returning to the guy he shot, he leans down with the pistol in his hand, as if to pistol-whip the guy. In the second flashback, it shows the same scene with Derek approaching but this time, when he gets to the guy, he just drags him into the street. This is intentional. The first version would have been what was heard in court (Danny did not testify) and what the jury would have heard from the defense. The gang members were on his property and this would show justifiable action on Derrick's part to get him the 3 year manslaughter charge. When it shows the scene again, it shows seeing Danny's actual recollection of what happened.
The punk band Anti-Heroes sued New Line Cinema over a character's tattoo featuring the band. The band did not want to be associated with Nazis, even fictional ones, in any way. The band went on to record a song called "NLC" that debases the film studio.
Edward Norton was said to have re-edited the film to lengthen his screen time. Director Tony Kaye then attempted to get his name removed but violated a Directors' Guild of America rule that states that directors that use pseudonyms (such as "Alan Smithee") must not talk about why they had their name removed - which Tony Kaye had done in ads in Variety. According to Entertainment Weekly, he then wanted his credit to read "Humpty Dumpty". Eventually, Kaye sued the DGA and New Line Cinema for $200 million ($275 according to the book Cinematic Century) stating that the DGA rule violated his first amendment rights.
In the midst of the dispute about the time he was taking to edit the film, Director Tony Kaye attended a meeting with Michael De Luca (then New Line's senior product president). Kaye arranged for a Rabbi, a Catholic priest and a Buddhist monk to be present at the meeting to support his argument and "make the meeting a more spiritual one".
The trivia items below may give away important plot points.
The original ending was of Derek standing in front of a mirror, shaving his head after Danny was shot. This was to make sense of the endless cycle of violence and tie the otherwise disjointed plot together but was removed after Edward Norton objected.