As the final month of the NFL’s regular season begins, the league’s response to concerns over a link between football and traumatic brain injury may finally be making a difference on the field, according to a FRONTLINE analysis of officially reported head injuries. Through the first 13 weeks of the season, a total of 96* concussions have been disclosed on team injury reports, down from 115 at the same point last season and 128 in 2012. At the current pace, teams are on track to report at least 122 concussions, a drop of nearly 20 percent from a year ago.