NFL lawyer Paul Clement argued that teams bear the chief responsibility for health and safety under the contract, along with the players' union and the players themselves.
"The clubs are the ones who had doctors on the sidelines who had primary responsibility for sending players back into the game," Clement said after the hearing.
The players argued that the league glorified violence through NFL Films, thereby profiting from dangerous hits to the head.
Players' lawyer David Frederick also accused the league of concealing studies linking concussions to neurological problems for decades, in part by hiring a rheumatologist to lead the Mild Traumatic Brain Injury Committee, which was created in 1994.
"It set up a sham committee designed to get information about neurological risks, but in fact spread misinformation," Frederick argued.
In recent years, a string of former NFL players and other concussed athletes have been diagnosed after their deaths with chronic traumatic encephalopathy, or CTE, including popular Pro Bowler Junior Seau and lead plaintiff Ray Easterling. Both committed suicide last year.
About one-third of the league's 12,000 former players have joined the litigation since Easterling's suit was filed in 2011.
Brody, during the oral arguments, pondered whether NFL head injuries belong in arbitration under terms of the contract.
"It has to be really specific," she said. "That's what I have to wrestle with."
REDSKINS: In other NFL court-related news Monday, a former Redskins player is suing the team, saying his career-ending knee injury resulted from a bounty program in which the team's coaches encouraged players to intentionally injure opponents.
Barrett Green played linebacker for the Detroit Lions and New York Giants between 2000 and 2005. He says a career-ending knee injury during a game on Dec. 5, 2004 was the result of an "unusual, outrageous and an obvious cheap shot."
The lawsuit also names former Redskins player Robert Royal, the player who hit Green, and former assistant coach Gregg Williams.
Green initially filed his lawsuit in May in state court in Maryland. It has since been removed to federal court in Greenbelt, Md.
The Redskins declined to comment on the case.