At one point during a street chase, Jimmy (Liam Neeson), runs past a billboard for Mad Max: Fury Road (2015). That film was also produced by the same studio (Warner Bros.), was scored by the same composer (Junkie XL), and the trailer for the film was attached to all release copies of this film.
During the bar scene, Liam Neeson mentions having a drink with Mickey Featherstone. In real life, Mickey Featherstone was a member of the New York City Irish-American gang called The Westies, based out of Hell's Kitchen.
The car that Jimmy Conlon (Liam Neeson) drives, is the same type of car that Patrick Swayze's character Truman Gates drives, in Next of Kin (1989). It was also a movie, in which Neeson starred, playing Swayze's brother.
Joel Kinnaman and Liam Neeson have both starred in a DC Comic Book movie featuring Batman. Joel Kinnaman starred as Rick Flag in Suicide Squad (2016), but doesn't share any scenes with Batman. Liam Neeson starred as Ra's al Ghul in Batman Begins (2005) and has a major role in the film, first as a type of mentor, and then later enemy. Common also had a small role as Monster T in Suicide Squad (2016). He also does not share any scenes with Batman, but shares a scene with Batman's most notable enemy, The Joker. Joel Kinnaman's character shares scenes with the Batman villains, Deadshot, Harley Quinn, and Killer Croc.
Joel Kinnaman and Liam Neeson have portrayed characters in the DC universe. Neeson played Ra's al Ghul in Batman Begins (2005) and The Dark Knight Rises (2012), and Kinnaman played Rick Flag in Suicide Squad (2016).
The trivia items below may give away important plot points.
Mike tells Eddie that Roy DeMeo's boys killed Billy. Roy DeMeo was a real hitman for the Gambino family, in charge of his own crew. Ironically Roy DeMeo was murdered by his own crew at mob boss Paul Castellano's orders.