The license plate of the car that picks up Tiger Chen, N666L4, refers to the fourth circle of Hell in Dante's Inferno; Greed.
Keanu Reeves' directorial debut.
Keanu Reeves and Tiger Hu Chen had previously worked together on The Matrix Reloaded (2003) and The Matrix Revolutions (2003).
Tiger Chen really did dislocate his shoulder during one fight. Which prompts Chen to say that in real-life, it was his right shoulder, not left, which was dislocated.
The correct spelling of Tai Chi is T'ai Chi. T'ai Chi is shortened for T'ai Chi Ch'uan and the meaning of it is "Supreme Ultimate Fist".