Update 08/19/2019 9:36pm:

The saga between Antonio Brown and the NFL over the star wide receiver being able to wear the specific helmet of his choosing is dragging on. According to Sports Illustrated, AB has filed a new grievance against the league over their ruling against his use of an old helmet that no longer passes the league's safety requirements. 

In Brown's latest grievance, he's arguing that he should be afforded the one-year grace period to phase out wearing his old helmet, a privilege that was granted to other players. This new filing comes on the heels of the Oakland Raiders' general manager Mike Mayock drawing the proverbial line in the sand. Mayock told reporters over the weekend after Brown missed practice, "from our perspective, it's time for him to be all in or all out."

NFL Network's Ian Rapoport reported that Brown's grievance will be looked over by an arbitrator on an expedited basis.

Update 08/12/2019 4:43pm:

Antonio Brown has been going against the NFL after they banned the old helmet that he wanted to use. Now, Brown is saying that he will hold the NFL liable if he was to get injured in the new headgear. Sources who are close to the grievance hearing said Brown would “hold the league liable” if he suffered any type of head injury from the new helmets the league is looking to implement.

source: The Athletic 

Original 08/09/2019 8:04pm:

Oakland Raiders star wide receiver Antonio Brown is threatening retirement if he is not allowed to wear his old helmet, a type of helmet that has recently been banned by the league. The helmet Brown is filing a grievance with the league over is no longer approved by NOCSAE (National Operating Committee for Standards and Athletic Equipment). An arbitrator is scheduled to look over the filing and make a decision next week. 

ESPN's Adam Schefter broke the story via Twitter, writing: "Raiders’ WR Antonio Brown has told team officials that, unless he gets to wear his old helmet, he will not play football again, per league sources." "Antonio Brown believes the new helmet that the rules mandate he wears protrudes out and interferes with his vision as he tries to catch football. The Raiders have been sending Brown other approved helmets to try out but, at this time, he is not interested in wearing any of them," Schefter added. 

Source: espn.com