Even in a sport where early retirements are all the rage in recent seasons, this one shocked the NFL world. On Saturday night, ESPN’s Adam Schefter reported that Indianapolis Colts quarterback Andrew Luck had informed the team he was retiring because he was “mentally worn down”:

Filed to ESPN: Andrew Luck has informed the Colts he is retiring from the NFL, per source. There will be a press conference Sunday to make it official, but Luck is mentally worn down, and now checking out. — Adam Schefter (@AdamSchefter) August 25, 2019

(And here we were thinking that Antonio Brown was the NFL superstar most likely to retire abruptly this preseason…)

Luck, who won’t turn 30 until September, had already compiled one of the greatest-ever starts to a quarterback career. The No. 1 overall pick from the 2012 draft picked up the reins from the recently departed Peyton Manning in Indianapolis and immediately led the Colts to the playoffs in his first three seasons, reaching the AFC Championship in the 2014 season. But injuries soon disrupted his storybook narrative. He missed more than half of the 2015 season with a string of injuries and all of 2017 after undergoing shoulder surgery. Prior to Saturday’s announcement, he had sat out all of preseason due to a lingering leg injury.

When he was on the field, though, the numbers spoke for themselves. Through his age-29 season, Luck already had the 84th-most yards, 68th-most touchdowns and 95th-most Approximate Value (AV) of any passer in NFL history. Just looking at seasons before age 30, Luck had about the same AV as John Elway, Joe Montana and Tom Brady:

Luck’s career was off to an all-time great start Best quarterbacks through their age-29 season according to Approximate Value, 1960-2018 Rank Quarterback Seasons Games Starts Total AV Per 16 Starts 1 Peyton Manning 1998-05 128 128 133 16.6 2 Cam Newton 2011-18 123 122 122 16.0 3 Fran Tarkenton 1961-69 126 119 121 16.3 4 Dan Marino 1983-90 119 117 114 15.6 5 Brett Favre 1991-98 113 109 109 16.0 6 Matt Ryan 2008-14 110 110 101 14.7 7 Matthew Stafford 2009-17 125 125 100 12.8 8 Russell Wilson 2012-17 96 96 100 16.7 9 Drew Brees 2001-08 107 106 95 14.3 10 Ben Roethlisberger 2004-11 114 113 95 13.5 11 Drew Bledsoe 1993-01 124 123 91 11.8 12 Daunte Culpepper 1999-06 85 84 91 17.3 13 Ken Anderson 1971-78 104 96 89 14.8 14 Boomer Esiason 1984-90 101 93 89 15.3 15 Joe Namath 1965-72 91 85 89 16.8 16 Steve Grogan 1975-82 99 92 88 15.3 17 Steve McNair 1995-02 103 95 88 14.8 18 Aaron Rodgers 2005-12 85 78 88 18.1 19 Randall Cunningham 1985-92 97 85 86 16.2 20 Philip Rivers 2004-10 84 80 84 16.8 21 Joe Flacco 2008-14 112 112 83 11.9 22 Neil Lomax 1981-88 108 101 82 13.0 23 Jim Zorn 1976-82 94 92 81 14.1 24 Troy Aikman 1989-95 98 98 80 13.1 25 Tom Brady 2000-06 96 94 80 13.6 26 Bob Griese 1967-74 94 90 80 14.2 27 Donovan McNabb 1999-05 94 88 80 14.5 28 Joe Montana 1979-85 103 79 80 16.2 29 John Elway 1983-89 100 98 79 12.9 30 Bert Jones 1973-80 83 77 79 16.4 31 Andrew Luck 2012-18 86 86 79 14.7 32 John Hadl 1962-69 112 82 78 15.2 33 Dan Fouts 1973-80 96 89 74 13.3 34 Terry Bradshaw 1970-77 97 87 73 13.4 35 Andy Dalton 2011-16 93 93 73 12.6 Seasonal age is as of Dec. 31 of the season in question. Source: Pro-Football-Reference.com

And that number might be understating Luck’s value. Because he missed so many games, he averaged 14.7 AV per 16 starts through age 29, the 19th-most of anyone on the list above, and more than contemporaries like Drew Brees, Ben Roethlisberger and Brady.

Luck shined in other metrics as well. As ProFootballFocus noted after the news of Luck’s retirement, he was a fixture atop their player grades, which try to measure player performance independent of teammate contributions. (Last season, he ranked third in the NFL behind Brees and Patrick Mahomes.) According to ESPN’s Total Quarterback Rating, Luck ranked fifth last season; for their part, Football Outsiders ranked him seventh in total value.

We’ve seen stars at other positions, like wide receiver Calvin Johnson (who retired after his age-30 season) and tight end Rob Gronkowski (age 29) walk away from the NFL in their primes. But it is exceedingly rare for a quarterback of Luck’s caliber to leave the game before age 30. If we limit our ranking above to quarterbacks who never played another game after their age-29 season, Luck has the second-most career AV, coming in ahead of former 49ers QB Colin Kaepernick — whose exile from the NFL was not by choice — and trailing only ex-Cardinals starter Neil Lomax:

It’s hard to find historical comparisons for Luck’s retirement Best quarterbacks through their age-29 season (according to Approximate Value) who didn’t play again after age 29, 1960-2018 Rank Quarterback Seasons Games Starts Total AV Per 16 Starts 1 Neil Lomax 1981-88 108 101 82 13.0 2 Andrew Luck 2012-18 86 86 79 14.7 3 Colin Kaepernick 2011-16 69 58 49 13.5 4 Josh Freeman 2009-15 62 61 41 10.8 5 David Woodley 1980-85 58 53 37 11.2 6 Pat Haden 1976-81 65 55 36 10.5 7 Vince Young 2006-11 60 50 36 11.5 8 Joey Harrington 2002-07 81 76 33 6.9 9 Tim Couch 1999-03 62 59 32 8.7 10 Steve Fuller 1979-86 90 42 32 12.2 Seasonal age is as of Dec. 31 of the season in question. Source: Pro-Football-Reference.com

Unlike Kaepernick, who probably still could play if given the chance (hello, Colts?), Lomax was forced to retire young because of an arthritic hip. He’s not a player many remember nowadays, but he was a Pro Bowler twice, and he led the NFL in passing yards in 1987. Beyond him, Luck and Kaepernick, it’s hard to find any other comparable examples of good QBs who never played a down in their 30s. That’s a big part of what makes Luck’s abrupt decision to walk away from the game on the eve of the 2019 season so surprising.

Now the Colts will have to move on without one of the best quarterbacks in the league. With Luck — and his +208 QB rating (relative to a replacement-level undrafted rookie) in our new quarterback-adjusted Elo rating system — we had the Colts rated as the ninth-best team in the NFL, with a 1564 rating (which roughly equates to 9.2 wins per 16 games against a typical schedule). Now they’ll be left with Jacoby Brissett, whose Elo value over replacement is +108. That drop-off leaves the Colts rated with a 1479 Elo, which ranks only 21st in the league and carries an expectation of 7.5 wins against an average schedule.

But Luck ultimately made his decision, which he called the hardest of his life, because he had lost his love for the game. “I haven’t been able to live the life I want to live,” he said Saturday night. “It’s taken the joy out of this game … the only way forward for me is to remove myself from football.” The result is a huge loss — for the Colts, but also for a league that will be missing one of the most promising young quarterbacks to ever play the game.