In Chicago-style softball, fielders do not wear gloves. The ball is 16 inches in circumference and mushier than the standard, 12-inch version. Practitioners of the century-old Midwestern ritual -- which enjoyed local television exposure in the 1990s -- believe it is the sport's purest form.

There's even a 16-inch Softball Hall of Fame, on West Harrison Street in Forest Park, Ill. It's open four hours each week, on Saturday afternoons. John "Duke" Gregerson was inducted with a lifetime batting average above .600. He played in more than 5,000 games. But his greatest joy in sports came as a fan, supporting the career of his son, Luke.

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Luke Gregerson played college baseball at St. Xavier University, an NAIA school in Chicago. Duke was a fixture at those games. Luke earned his degree in criminal justice with a minor in business management. He took the LSAT and made plans to attend John Marshall Law School in Chicago. But then the Cardinals drafted him in the 28th round of the 2006 Draft, and what's the harm in delaying law school?

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Gregerson, would-be attorney-at-law, still hasn't taken contracts or torts. He made the Padres' Opening Day roster in '09 and steadily assumed greater responsibility in the San Diego bullpen. He reached the postseason with the A's in '14, and then he signed a three-year, $18.5 million deal to become the Astros' closer.

At every milestone, a grinning Duke would nudge his nephew and confidante, Ron Kelly, and say with the same humility and awe: "Can you believe this?" And the greatest of those moments came four years ago, when Luke was selected to pitch for Team USA at the World Baseball Classic.

"When I told him, he overnighted the Team USA jersey to himself," Luke recalled in a telephone interview over the weekend. "By the next day, he'd texted me a selfie of him wearing it. He wore that jersey all the time."

The jersey traveled with Duke to Phoenix and Miami, as he watched his son throw two scoreless innings for the national team. Then last December, Luke received a text message from U.S. general manager Joe Torre: Would he have interest in pitching for Team USA again in WBC '17?

Gregerson would be one of five returning U.S. players -- and the only pitcher. He answered Torre immediately: "Sign me up."

Three weeks later, Duke Gregerson died of brain cancer. He was 60.

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The Gregerson family remains in mourning, two months after Duke's death on New Year's Day. For his wife, Cindy, and children, Amy, Luke, Scott, Lisa and Heidi, the void is especially profound because of the selfless way in which he lived.

"To know Duke was to love him," said Ron Kelly, the nephew with whom he was inseparable, on and off the softball field. "He saw the good in everything. He was a man's man. You trusted him. He was a man of action, more than a man of words. Don't get me wrong: He'd always have kind words to say. But you generally looked at what he was doing."

During that legendary career on Chicagoland softball fields, Duke always wore jersey No. 18. His son, wanting to respect his father's legacy, chose different numbers: No. 57 with the Padres, No. 44 with the A's and Astros.

But in the days after Duke's passing, Ron texted Luke with an idea: Wouldn't it be great to honor your dad by wearing 18 for Team USA?

Luke's reply buzzed immediately.

Already am.

Ron put down his phone. And cried.

"I've worn 'Duke' on my glove ever since I started playing baseball, but I've never had 18," Luke explained. "As soon as I found out I would be on the team again, I called someone at USA Baseball about getting that number."

While some Major League players and fans remain uncertain how to feel about the World Baseball Classic, there's been no ambiguity for the Gregersons.

"I will tell you our family is exceptionally patriotic," Ron said. "I can remember being in Arizona four years ago, sitting with my uncle and all of his in-laws. [Duke] turned to me and said, 'My son is representing the United States of America. It doesn't get any better than this.'

"If you could've crawled into my uncle's heart, you couldn't have found a prouder person in the world at that moment."

And we can say that Duke Gregerson lived the American Dream because, well, he did: He worked as a boilermaker for 18 years, then another 22 as the chief maintenance engineer of a 32-building condominium complex in the Chicago complex. He had a reputation for being able to fix anything. But his passion was sports -- specifically, the softball he played and baseball he watched.

"He loved baseball more than anyone I've met in my life," Luke said. "He lived and breathed playing it and watching it. Coming to the games to watch me play was a big part of his life. He had this great, big smile on his face, every time he was around baseball."

The game aided Duke's legendary defiance of the disease. When he was first diagnosed, doctors gave him three months to live. He lasted 19. Remarkably, he returned to the softball field -- with a three-hit game -- after undergoing brain surgery.

Stubbornly and inspirationally, Duke played seven months of softball following the terminal diagnosis.

"Mentally and physically, he was an incredibly strong man," Luke said. "Everybody knew that. When we played football as a family, he would go 100 percent at all times. He was very competitive -- and also very loved and respected. He didn't take anything for granted. And he went about this whole situation the same way.

"He put up a great fight until the very end. Cancer is just a disgusting, terrible thing. In the end, it got the best of him."

Duke's health deteriorated during the '16 season, but the emotional hardship wasn't evident in Luke's performance. His WHIP was under 1.000 for a second consecutive year. When the season was over, Gregerson had made at least 50 appearances, with an ERA below 3.50, for an eighth straight season. Only one other Major League pitcher, Brad Ziegler , has done the same since '09.

Dependability always was a Duke Gregerson hallmark.

"At the end of the day, he didn't want me to stop pitching," said Luke, who was placed on the bereavement list for one series in '16 to spend time with his father. "He would've been upset if I [stayed home]."

Luke didn't play in the postseason in '16, but Duke's favorite childhood team -- the Cubs -- were decidedly involved. Ideally, Duke would've attended Game 7 in Cleveland with Ron. Instead, Ron and Luke went together. And although Duke was in failing health, Luke said his father was cognizant of having lived to see the Cubs win their first world title in 108 years.

Team USA's wait to win the World Baseball Classic has been less than one-tenth of that, but let's remember which jersey Duke Gregerson cherished the most. In fact, it was after the '13 Classic that a beaming Duke told Ron, "I need to show you something." There, in his house, was a U.S. jersey signed by every member of the '13 national team.

Perhaps in a few weeks, one final jersey will join Duke's collection: a new set of signatures surrounding GREGERSON 18 in red, white and blue.

Jon Paul Morosi is a columnist for MLB.com.