Film producer Dan Lin claims the two stars trained for their fight scene in the movie by sparring at Penn's home after director Reuben Fleischer told his leading men he wanted the scrap to look as real as possible.
Lin tells HollyScoop.com, ""They would train in front of Sean's front yard once in awhile. I mean, they really got into it.
""Sean and Josh are in tip top shape and they really train... It (fight scene) looks so visceral and real and makes our climax really exciting.""
Brolin, who plays a tough 1940s cop in the film, recently admitted the brawl scenes were challenging to shoot because Penn, who portrays Mafia boss Mickey Cohen, had not perfected the fight choreography.
He told WENN, ""The fight I did with Sean Penn (was the most challenging scene). He didn't rehearse as much as I did so his fists were flying wildly during the fight, hoping they (camera operators) got something that was usable. It was a tough fight and I love the way that it turned out, but I think for both of us being the current and ex smokers that we are, that was the most challenging on an oxygen level.""