Carolina Panthers linebacker Luke Kuechly announced his retirement Tuesday after eight seasons.

The 28-year-old was coming off another Pro Bowl year where he amassed 144 tackles in 16 starts and tied his career high of 12 passes defended.

More importantly, Kuechly was a universally respected player on and off the field, with scores of teammates and opponents offering kind words after the announcement, including Panthers tight end Greg Olsen and New Orleans Saints wide receiver Michael Thomas.

The Pro Football Hall of Fame will assuredly be calling Kuechly's name someday after an excellent career that surprisingly ended Tuesday.

Shocking retirements aren't uncommon in the NFL, where the physical and mental brutality of the game has forced some of the game's greats to end their career.

Here's a look at some of those decisions, led by two from within the last six months in Kuechly and ex-Indianapolis Colts quarterback Andrew Luck.

Luke Kuechly

"There is only one way to play this game since I was a little kid is to play fast and play physical and play strong, and at this point I don't know if I'm able to do that anymore," Kuechly said.

"... I still want to play, but I don't think it's the right decision."

Kuechly was excellent once again in 2019, and there's reason to believe that would have been the case in 2020 given his fantastic resume.

However, Kuechly said he thought about the decision "for a long time" and also noted that his call had nothing to do with recent coaching changes.

Kuechly's stellar career included seven Pro Bowls, five first-team All-Pro nods, a Defensive Player of the Year award and a Super Bowl 50 appearance.

Andrew Luck

Luck suffered numerous significant injuries during his career, as Zak Keefer of The Athletic noted:

Those injuries naturally took a toll on Luck's psyche, which the quarterback referenced in an August 24 presser after a Colts preseason game.

Luck missed the entire 2017 season but came back in 2018 with 39 touchdowns and a career-high 67.3 completion rate. He won the Comeback Player of the Year award, and expectations were high for the Colts heading into 2019 following an appearance in the AFC Divisional Round.

However, an ankle issue that kept Luck off the practice field lingered into the preseason, to the point where it still hadn't improved by the time the quarterback made his decision.

Luck retired at the age of 29 after making four Pro Bowls.

Barry Sanders

Hearing ex-Detroit Lions running back Barry Sanders talk about his sudden retirement provides much clarity about his decision, but it was still shocking in 1999 following another excellent individual season.

As explained in his 2003 autobiography (h/t Associated Press, via ESPN), Sanders was upset that Lions management didn't seem particularly motivated or able to build a winning team around him.

Sanders, who played in Detroit from 1989 to 1998, was on four Lions teams that finished 6-10 or worse. Detroit went 9-7 in 1997 but slumped to 5-11 in 1998 with little hope in sight.

Still, the decision was eye-opening for a player who had just gained 1,780 yards from scrimmage in his 10th Pro Bowl year.

In hindsight, Sanders' call makes perfect sense.

Sanders is a six-time All-Pro, a three-time AP Offensive Player of the Year and the co-winner of the 1997 NFL MVP. He made the Pro Football Hall of Fame in 2004.

Calvin Johnson

Like Sanders, Johnson called it a career with the Lions while still in his prime.

Like Sanders again, Johnson cited the state of the Lions as a reason for his departure.

The 2015 Lions came off an underwhelming season and didn't appear very close to a Super Bowl win. Johnson desired a move to a team with better championship aspirations, but Detroit would not release him from his contract.

"I was stuck in my contract with Detroit, and they told me, they would not release my contract, so I would have to come back to them," Johnson said, per ESPN.

"I didn't see the chance for them to win a Super Bowl at the time, and for the work I was putting in, it wasn't worth my time to keep on beating my head against the wall and not going anywhere."

And thus Johnson retired. He also said that, plus "the body," was the reason for his decision. He told Michael Rosenberg of Sports Illustrated in September 2019 that he suffered nine concussions.

The former No. 2 overall pick played from 2007 to 2015. He had 88 catches for 1,214 yards and nine touchdowns in his final season.

The six-time Pro Bowler and three-time All-Pro led the league in receiving yards twice. He'll be eligible for the Hall of Fame in 2021.

Jim Brown

The ex-Cleveland Browns running back and the greatest player in NFL history by many accounts called it a career after just nine seasons, but the reasons were different than most players on this list.

In Brown's own words to then-Browns owner Art Modell:

"I am writing to inform you that in the next few days I will be announcing my retirement from football. This decision is final and is made only because of the future that I desire for myself, my family and, if not to sound corny, my race. I am very sorry that I did not have the information to give you at some earlier date, for one of my great concerns was to try in every way to work things out so that I could play an additional year."

Brown was being fined $100 per day for not being at the team's 1966 training camp. At that point, the running back was looking at a post-football career, which included acting. He was shooting his role as part of the film The Dirty Dozen in London at the time, per Ryan Cortes of The Undefeated.

Brown's 104.3 career rushing yards per game stands as an NFL record. He made nine Pro Bowls and eight All-Pro teams and won three MVPs. His final season saw him gain 1,872 scrimmage yards and score 21 touchdowns in just 14 games.

Brown also led Cleveland to the 1964 NFL title.

Earl Campbell

Few (if any) running backs took more of a physical toll in a shorter time span than Earl Campbell, who was the ultimate bell cow in an era where the game was far more brutal than it is today.

Campbell averaged 369.8 touches per season during the first four years of his NFL career with the Houston Oilers. He ended his career with the New Orleans Saints.

Campbell retired during the 1986 preseason, a move that apparently took New Orleans by surprise. But Campbell's body had taken a beating over the years, leading to the decision.

"I'm a man; I'm not a little boy," he said. "I believe this is the best thing—not only for myself, but for the Saints."

Campbell rushed for 4.1 yards per carry for the 1985 Saints as part of a timeshare backfield with Wayne Wilson.

Campbell was the league's 1979 NFL MVP. The five-time Pro Bowler and three-time Offensive Player of the Year was inducted into the Pro Football Hall of Fame in 1991.

Roger Staubach

It's not often that you see future Hall of Famers retire after posting career-best numbers, but Dallas Cowboys legend Roger Staubach was forced to do so after the 1979 season.

Somehow, Staubach posted career highs with 27 touchdown passes and 224.1 passing yards per game en route to leading Dallas to an NFC East title.

But the injuries mounted for Roger the Dodger, who somehow missed just two regular-season games from 1973 to 1979.

Per Paul Zimmerman of Sports Illustrated, Staubach suffered five concussions during his final season and 20 in his football career. He also suffered at least 17 left shoulder dislocations.

Staubach retired in April 1980 and handed the quarterback keys to Danny White. He left the game as a two-time Super Bowl winner, a six-time Pro Bowler and the 1978 Walter Payton Man of the Year winner. He made the Hall in 1985.