The New England Patriots were suddenly without safety Patrick Chung when they took to the field for the second half against Jacksonville on Sunday.

Chung, a versatile defensive back and captain, was taken off the field briefly in the first half before going back in. However, the Patriots announced in the third quarter that Chung had been removed from the game.

What happened? The NFL and NFL Players Association are launching a joint investigation to figure it out, according to ESPN’s Mike Reiss.

Chung was slow to get up after a play early in the second quarter, triggering an injury timeout. USA Today reported umpire Barry Anderson spoke with Chung after the play and directed him to the sideline. Chung returned to the field one play later.

The decision to flag a potential concussion is not in the hands of teams or officials. Instead, it is handled by a team of independent spotters appointed by the NFL, who can flag potential head injuries and pull players out of the game for evaluation.

During a conference call with reporters Wednesday, Patriots Coach Bill Belichick declined to comment on the status of Chung and Trey Flowers (who also suffered a concussion in Sunday’s game).

The Patriots have not given an update on Chung or Flowers. The first official update on their statuses should come from the first practice report of the week, which is set to be released Wednesday, as required by the league.

LIONS: Detroit waived offensive lineman Jamil Demby, a rookie from the University of Maine taken in the sixth round of the draft by the Los Angeles Rams. Demby was released by the Rams and awarded to the Lions via waivers last week. He was inactive for Sunday’s loss at San Francisco.

A GROUP OF Pro Football Hall of Famers is demanding health insurance coverage and a share of NFL revenues or else those former players will boycott the induction ceremonies.

In a letter sent to NFL Commissioner Roger Goodell, NFLPA Executive Director DeMaurice Smith and Hall of Fame President David Baker – and obtained by The Associated Press – 21 Hall of Fame members cited themselves as “integral to the creation of the modern NFL, which in 2017 generated $14 billion in revenue.”

Among the signees were Eric Dickerson, listed as chairman of the newly created Hall of Fame Board the group has formed, Jim Brown, Jerry Rice, Joe Namath, Lawrence Taylor, and Sarah White, the widow of Reggie White.

The strongly worded letter called out the league for paying Goodell $40 million, saying “there are better uses for that money.” It also criticized Smith for his salary and the lack of a former player on the players’ association board. But there have been two former players on that executive board since 2009.

CHARGERS: Los Angeles defensive tackle Corey Liuget has sued the trainer who he says is responsible for his four-game suspension for using a performance-enhancing substance.

Liuget filed suit against Ian Danney and his Arizona-based business in Los Angeles, asking for a jury trial and no less than $15 million in damages.

Liuget says in the suit that Danney injected him with a substance banned by the FDA and the NFL. He also says Danney gave him another product that required a prescription which Liuget did not have.

VIKINGS: Minnesota signed kicker Dan Bailey as a replacement for rookie Daniel Carlson.

Bailey, 30, owns the second-best field goal percentage in NFL history, making 186 of 211 field-goal attempts. Bailey slumped last season after a groin injury that kept him out for four games.

Minnesota waived Carlson after he was 0 for 3 at Green Bay Sunday with the last two failed tries coming in overtime and forcing the Vikings to settle for a 29-29 tie with the Packers.

BEARS: Khalil Mack had one of six sacks, Prince Amukamara returned an interception 49 yards for a touchdown and Chicago beat Seattle 24-17 Monday night to give Coach Matt Nagy his first win.