Ex-New Orleans Saints running back Pierre Thomas says he personally tried to stop the road rage altercation involving his friend Will Smith ... but he was too late.
Thomas has been called as a witness in the murder trial of Cardell Hayes -- the man who shot Smith during the incident in New Orleans on April 9th.
Thomas was in one of the three cars in Smith's caravan -- which included several people who had eaten dinner together at a New Orleans restaurant earlier in the evening.