NFL Players Association president JC Tretter is calling for NFL teams to change all field surfaces to natural grass to reduce the risk of injury to players.

Players have a 28% higher rate of noncontact lower extremity injuries when playing on artificial turf as compared to grass.

"The data stands out," Tretter said Wednesday during a videoconference with media. "Those numbers are staggering, the difference in injury rate between turf and natural grass. It's possible to get grass in every location, and it's about pushing for that. We all should be working toward the safest style of play. We know the dangers of playing on turf. That's not good for anybody. It's not good for players. It's not good for the GMs and the head coaches. It's not good for the owners. It's not good for the fans. Increased injuries isn't good for anybody.

"Until we can find a way to get synthetic turf to respond and react like natural grass, it's too much of a danger to continue to play on and expect different results."

Thirteen NFL stadiums use artificial turf.