The N.F.L. has taken measures in recent years to detect concussions by placing unaffiliated neuro-trauma consultants on the sideline, adding spotters in the press box and permitting medical personnel to call a timeout if the on-field staff misses a possible head injury. Those advances contributed to the most diagnosed concussions the league has seen in four years, according to data released Friday.
But most of those improvements were in place last season, when concussions declined. A year after proclaiming how the incidence had decreased in each of the past three seasons, since 2012, members of the league’s medical community were left to determine what accounted for the spike.