Giants Hall of Fame linebacker Harry Carson struggled with the aftereffects of concussions during and after his 13-season career. He called 49ers linebacker Chris Borland's retirement after just one season a "courageous decision that most other people would not even give a second thought to.''

Carson was diagnosed with post-concussion syndrome shortly after his career ended in 1988. He commended Borland for "his quest for information and making a sound decision for himself. It is a sign of who he is as a person and that he's not just following the crowd. He is one who looks out for himself.''

Carson is among several former and current players to express support for Borland, 24, who said Monday he had decided to leave the NFL because of concerns about concussions.

He is the fourth NFL player 30 or younger to retire recently. The others are 49ers linebacker Patrick Willis, Titans quarterback Jake Locker and Steelers linebacker Jason Worilds. Only Borland cited concerns about the potential for problems related to head trauma.

Carson said he would have made the same decision Borland made if he'd had the same information about concussions. Carson said if he had to do it all over again, he never would have played football because of the physical problems he endured, particularly concussions.

"We didn't know, so Chris Borland was more fortunate than any of us were, whether we played one year or were 15-year veterans,'' Carson said. "Now [Borland] has all the information about concussions. You look at the players who have committed suicide, guys like Dave Duerson and Junior Seau. That's information that guys today have at their disposal to make an informed decision. We didn't have that.''

Borland had an excellent rookie season. He had 107 tackles, two interceptions and was NFL Defensive Player of the Week. He would have replaced Willis, a five-time All-Pro, as the 49ers' middle linebacker.

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"Got to respect Borland for clearly putting thought into his decision,'' Giants guard Geoff Schwartz wrote on Twitter. "If you're not 100 percent committed to this game, better to walk away.''

Rams defensive end Chris Long tweeted that Borland's decision took guts. "I loved Chris Borland's game but I can't fault him for calling it quits. His concerns are real. Still it takes a man to do the logical.''

Borland told ESPN's "Outside the Lines'' he had researched concussion issues and decided the best thing to do was to retire. He said he thought he had a concussion during training camp last season, but didn't tell anyone because he was afraid he wouldn't make the team.

"I just honestly want to do what's best for my health,'' he said. "From what I've researched and experienced, I don't think it's worth the risk. I just thought to myself, 'What am I doing?' Is this how I'm going to live my adult life, banging my head, especially with what I've learned and knew about the dangers?''

Jeff Miller, NFL senior vice president of health and safety policy, said in a statement that the league continues to make advances in player safety. He said concussions in NFL games were down 25 percent last season.

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"We respect Chris Borland's decision and wish him all the best,'' Miller said. " . . . By any measure, football has never been safer and we continue to make progress with rule changes, safer tackling techniques at all levels, and better equipment, protocols and medical care for players.

"We are seeing a growing culture of safety. Everyone involved in the game knows there is more work to do and player safety will continue to be our top priority.''