Will Smith, who calls himself a "football dad," admitted he was initially not on board with the idea of playing Dr. Bennet Omalu in "Concussion" and felt conflicted about playing a doctor who discovers football-induced brain trauma was the cause of death of some former National Football League (NFL) players, according to Reuters.

"Concussion" follows the story of Omalu, a Nigerian forensic neuropathologist who exposes the connection between brain damage and the deaths of several NFL players and the subsequent attempt by the league to to deny the problem and disparage Omalu.

"I'm a football dad," Smith said at the AFI Fest premiere in Los Angeles on Tuesday, according to Yahoo! Movies. "For me, [the role] was really conflicting. When I sat down with Bennet I was hoping, 'Please say something to make me not take this movie.'"

However, the "Focus" star said that he felt compelled by the story and his ignorance about the perils of the most popular sport in U.S. to play the part.

"I had watched my son play football for four years, and I didn't know," Smith said. "And just as a parent, I felt like I had to be a part of this. Bennet's quest for the truth... became our quest to deliver the truth, because people have to know."

"Concussion," which also stars Gugu Mbatha-Raw and Alec Baldwin, is slated to hit theaters on Dec. 25.

Watch the trailer below: