Even by N.F.L. standards — remember Deflategate, anyone? — the standoff between Oakland Raiders receiver Antonio Brown and the league is odd.

For the past few months, Brown has insisted that he be allowed to wear his favorite helmet even though the N.F.L. and the players association have determined it no longer meets their safety standards. Brown has sat out much of the preseason, filed two grievances and tied his new team in knots.

Brown was not the only player to complain when the league and the union announced their list of approved helmets in April. New England Patriots quarterback Tom Brady, Green Bay Packers quarterback Aaron Rodgers and other players also had to ditch their old helmets. But they eventually picked new models from the list of 34 approved helmets and moved on.

Brown is the lone holdout. He is so upset about not being able to wear the Schutt AiR Advantage, which was discontinued in 2011, that he filed a second grievance against the league on Monday, arguing that the helmet should be grandfathered in.