It was an unremarkable play during a unmemorable game, so innocuous that it doesn’t appear in the box score. But it wound up changing Twins history.

Joe Mauer has played his final game, a decision he announced Friday but one that can be traced back to that mid-May game in Anaheim. Trying to make a lunging catch on a foul pop fly just out of his reach, Mauer tumbled awkwardly to the ground. The St. Paul native got up and continued the game, but the impact had jarred his head and stung his neck. The diagnosis came within days: Another concussion.

Mauer, who had been forced to abandon his favored position as a catcher in 2013 by a series of concussions, sat out a month to recover, and played out the season, even finishing with a final-day flourish by catching one last pitch behind the plate. But with a wife and two daughters to consider, and another child on the way, that seemingly harmless foul ball forced an agonizing choice to give up the sport he loves for “what is best for me as a husband and a father.’’

Retirement, he said in a letter to fans posted on the Twins’ website, “came down to my health and my family. … If I were to continue playing this game, I would want to do so without reservation, and I no longer feel that is possible.”

The decision was not unexpected, not after the emotional parting between Mauer and Twins fans during the season’s final game. But it still was a jolt to his teammates, current and former, and those who watched him become a three-time batting champion, six-time All-Star, 2009 Most Valuable Player, and one of the greatest players in Twins history.

“He’s on the Twins’ Mount Rushmore,” said Glen Perkins, another Minnesota native and MLB All-Star who spent his entire career playing for the team he cheered on as a child. “After that last game, I texted him. I said, ‘Congratulations on a hell of a career.’ He texted back, ‘Not bad for two kids from Minnesota.’”

Not bad at all. Mauer, the first player chosen in the 2001 draft after a storied baseball, basketball and football career at St. Paul’s Cretin-Derham Hall High, reached Minnesota three years later and spent 15 seasons in the big leagues.

“He had the best swing I’ve ever seen by an amateur,” said Mike Radcliff, the Twins’ scouting director at the time, who recommended that the team select the hometown superstar. “Smooth, technical, balanced — an almost perfect baseball swing.”

Mauer used it to collect 2,123 hits, more than any Twin but Kirby Puckett. His 428 doubles are the most in Twins history. He batted above .300 eight times during his career, and in 2006 he became the first AL catcher ever to win a batting title, putting up a .347 average.

His .328 average in 2008 earned him another batting title, and his career best .365 average, along with 28 home runs and 76 RBI, made him the fifth Twin ever elected MVP. He was also awarded three Gold Gloves as the league’s best defensive catcher, and became a national star featured in advertisements for Head and Shoulders and PS3 video consoles. “Well played, Mauer,” became a viral catchphrase, uttered in a video game commercial in 2010.

But if his game was attention-getting, Mauer tried to avoid the spotlight off the field.

“You never heard a single bad thing about Joe. He was happiest when he could go unnoticed,” said pitcher Jake Odorizzi, Mauer’s teammate through his final season. “But he was a joy to play with and get to know in the clubhouse. I wish I would have had the chance to throw to him as a catcher.”

If not for the concussions, Odorizzi figures, “he could play for another five years at a high level, maybe more.”

Maybe so, but Mauer, whose eight-year, $184 million contract expired last month, made it clear that his wife, Maddie, 5-year-old daughters Maren and Emily, and the baby due later this month, are more important.

“I find myself thinking about my future health, and its impact on my family, more than I had years ago. People always told me how much things change when you become a parent, and they were right,” Mauer wrote in his farewell letter.

“There is a part of me that will always want to compete, but I have reached a point where my desire to play is outweighed by the possibility of another injury.”

Terry Ryan was the Twins general manager who approved the decision to draft Mauer with the first pick in 2001.

“It’s a shame that he couldn’t stay behind the plate, and it’s a shame that [concussions] cut short his career,” Ryan said. “But we’re all human beings first, husbands, fathers. He had a marvelous career, but baseball comes in behind every one of those. And that last day — what a way for him to go out.”

It was a farewell, in a Sept. 30 game with the White Sox, that neatly summed up his career. His daughters joined him at first base for the national anthem. He blasted a line drive in the seventh inning for a double, his final hit. And Mauer brought the large Target Field crowd to deafening cheers and heartfelt tears in the ninth, when he appeared on the field in his catcher’s gear for the first time in five years.

After a raucous ovation, he squatted behind the plate, caught one last pitch, hugged pitcher Matt Belisle, and headed off, we now know, into retirement.

He realized it, too.

“The answer I was searching for came into sharper focus during my last game, a game I will never forget and a day where I felt like everything I was questioning started to become clear,” Mauer wrote. “As I stood on the field in my catcher’s gear, something I never thought would be possible again, I realized that this is how I wanted to finish my career.”