The rap battle scenes took days to film, and the 300 extras were starting to get bored. Director Curtis Hanson started an improv freestyle rap battle among them, and the three best rappers would be filmed going head-to-head with Eminem. Each of the 134 volunteers got fifteen seconds in front of the judiciary panel. Ultimately, the jury chose four rappers, who got a one-shot, one-take-only scene with Eminem, who wanted to mime his responses to save his voice for the scripted scenes. Eminem couldn't resist the challenge by staying silent, especially with the crowd taunting him, and took on his opponents.
Future is based almost entirely on Eminem's best friend Proof, from hosting the battles to the story of how he got his name. Proof also plays Lil' Tic, the rapper B-Rabbit faces in the first battle. Proof manages to sneak his name as an acronym when he raps, "I'll (P)unish (R)abbit (O)r (O)bsolete (F)uture."
Eminem was quite keen that the film not be an autobiographical piece, as he felt that homing in on his own personal history would limit the storytelling and characterization. By creating a fictional character, he knew that he would be unrestricted in how he performed.
Eminem was unable to accept his Academy Award in person. He felt so sure another nominee would win that he did not bother to attend the ceremony. Instead he was sleeping, while his daughter watched cartoons the night he won.
When Eminem lived in Detroit, he first started performing at Shelter, a Detroit club located in the basement of St. Andrews Hall. Scenes that take place at Shelter were filmed in an empty warehouse because the actual club looked too nice.
In the movie, Rabbit's mother states he got his nickname rabbit because, as a child, he had big ears like a bunny rabbit. In real life, Eminem's relatives called him "Mickey," in reference to "Mickey Mouse," for the same reason.
Proof, the inspiration for the character Future, was sought by producers to play that role in the film. However, Proof failed to show up for the audition and director Curtis Hanson decided that he wanted a more experienced actor to play Future. Proof was then cast in the smaller role of Lil' Tic.
8 Mile (2002) was originally considered to have an unofficial follow-up movie, titled "Southpaw," with Eminem reprising his role, now as a down-on-his-luck lightweight left-handed boxer trying to regain custody of his daughter. The script eventually evolved and that idea was scrapped. However, the film was eventually made and was released in 2015, with Jake Gyllenhaal starring in the lead role with Eminem producing the soundtrack.
In the last battle against Papa Doc, B-Rabbit says, "He's shook 'cause ain't such thing as halfway crooks." This is a reference to the instrumental playing in the background, from the rap duo Mobb Deep's "Shook Ones Pt. II." The chorus is, "There ain't no such thing as half-way crooks, scared to death, they scared to look, they shook." The same song is played in the opening scene, when Jimmy is practicing in the bathroom.
In the final battle, Future says that there are new rules, one of which is that each man gets a minute and a half to do his piece. This genuinely happens; from when Rabbit tells everyone from the 313 to put their hands up, to Future telling the DJ to cut the beat, exactly 90 seconds pass.
The trivia item below may give away important plot points.
Anthony Mackie goes on to the MCU as Falcon in Captain America: Winter Soldier, Ant-man, Captain America: Civil War. Michael Shannon goes on to the DC universe as General Zod in Man of Steel and Batman v Superman: Dawn of Justice (cameo).