NFL players may be wearing different helmets based on their position in the not-too-distant future.

The chairman of the league’s head, neck and spine engineering subcommittee outlined the research that’s leading in that direction in an informal gathering with reporters at the NFL owners meetings on Tuesday.

Dr. Jeff Crandall, director of the Center for Applied Biomechanics at the University of Virginia, said the NFL is working to develop reliable sensors to monitor the minute details of the impact of concussion-causing hits.

Once those sensors are developed, it soon could well be the case of big linemen and speedy receivers wearing helmets that protect different parts of the head.

“There are position-specific cleats, position-specific shoulder pads, and we know that players in different positions receive different types of severity and frequency of impacts,” Crandall said, “so we think that a position-specific helmet makes sense.”

Crandall repeated statistics first made public at the Super Bowl that showed concussions caused by helmet-to-helmet hits were down, and concussions caused by helmet-to-body hits were up. That would make sense as players shift from drilling an opponent’s helmet and hit the shoulder pad or lower instead.

That might lead to work to develop a safer shoulder pad as well as helmet, Crandall said.

Position-based helmets could be in use in four or five years.

Replay changes

NFL owners approved having referees use a hand-held tablet for video replay reviews and also centralized final decisions on such calls. Previously, the referee would go to a sideline camera for reviews, and he would have final say on keeping or reversal a call.

Now, league officiating chief Dean Blandino and his staff in New York will make those decisions with input from the referee.

Also Tuesday, owners extended bringing touchbacks out to the 25-yard line for another year, and eliminating “leapers” trying to block field goals or extra points. They added protections for defenseless receivers running their routes, too.

Witten signs deal

Dallas tight end Jason Witten has signed a four-year contract extension that virtually guarantees the 14-year veteran will spend his entire career with the Cowboys. The extension has a maximum value of $29 million. Witten turns 35 in May.

Agreements

The Philadelphia Eagles agreed to terms on a two-year contract with defensive end Chris Long, who won a Super Bowl last season with New England. … The New York Jets signed former Indianapolis Colts offensive lineman Jonotthan Harrison. Terms were not available. Harrison was not tendered a restricted free agent contract by the Colts earlier this month, making him an unrestricted free agent.