FORT WORTH, Texas — The average life expectancy for a male in the U.S. is 78 years. The average career for an NFL player is just under four years. Marion Barber’s NFL career lasted almost twice as long, while his entire life ended well short of the average male. On Wednesday in Frisco, the former Dallas Cowboys running back died at the age of 38. The cause of death is unknown. Whenever the coroner’s report is finished it should include as a probable cause of death the word “football.” We are kidding ourselves if we don’t think football contributed in some way to his death. “We are heartbroken …