The NFL will again ban non-traditional facemasks this upcoming season, saying that the masks consistently fail safety tests and are not up to the league's safety standards, reports NFL.com.
Banned facemasks have "more bars, smaller spaces between the bars, and a generally larger coverage area," NFL executive vice president of football operations Troy Vincent wrote in the memo.
Only four NFL players wore those kinds of masks last season, including new Oakland Raiders defensive end Justin Tuck, but any player who had medical approval was allowed to wear the masks. Those who want to continue wearing the masks in 2014 will need to be re-evaluated prior to the start of the season.
According to a league memo, the NFL says that based on research from the National Operating Committee on Standards for Athletic Equipment, the "non-standard facemasks more frequently fail safety and certification tests and aren't up to NFL safety standards."
The league instituted a similar rule before the 2013 season.
More from NFL.com:
A study conducted by the University of New Hampshire for the NFL states that the added weight of the masks negatively affects the structure of the helmet, can cause neck fatigue that could lead to a more head-down posture during contact and can provide a false sense of security during tackling.