Josh Brolin has come on board the documentary “Unchained: The Untold Story of Freestyle Motocross” as the narrator and will also executive produce the project.

“Unchained” is in post-production and will be introduced to worldwide buyers at the American Film Market by The Exchange.

The film, centered on the birth and boom of Freestyle Motocross (FMX), is produced, directed and written by Paul Taublieb, one of the creators of the X Games. Jon Freeman, who helped popularize the sport as a filmmaker, is the co-director and co-producer.

Taublieb directed the feature racing documentary “Fastest” and  “Hawaiian: The Legend of Eddie Aikau.” Freeman directed the video series “Crusty Demons of Dirt.”

“Unchained” includes Carey Hart, Tony Hawk, Travis Pastrana, Danny Way, Mike Metzger and Jeremy McGrath.

Executive producers are Susan Cooper, Brian O’Shea, Jeff Bowler and Nat McCormick. Brolin stars in current releases “Everest” and “Sicario” and will be seen next in “Hail, Caesar!”