ENGLEWOOD, Colo. — Packers-Bears is the matchup that the NFL chose to open its 100th season Thursday night. The league opted for the historical resonance of two teams whose histories date back to the NFL’s founding.

But Broncos-Raiders is the duel that will actually give a look into the NFL’s past.

This isn’t a story about the Broncos hiring Vic Fangio, a new head coach with an old-school demeanor. Nor is it about the Raiders tying their hopes for as many as 10 years to Jon Gruden, a coach who told a gaggle of media weeks after his January 2018 rehiring that “I’m trying to throw the game back to 1998.”

It’s all about the dirt.

The infield dirt.

This is likely to be the next-to-last game in NFL history played with a baseball infield devouring a massive chunk of the playing surface, barring an Oakland Athletics trip to the World Series. So when the Raiders face the Kansas City Chiefs on dirt six days after the Broncos visit, an era of NFL history will close.

“That’s crazy that it’s still happening in 2019, but, yes, we are playing on dirt. Still,” Raiders quarterback Derek Carr said. “And we love our dirt, that’s for sure.”

Good thing he does. Few others do.

Given that this week’s game is the final one that the Broncos will play in Oakland, multiple players were asked why it was so hard to play and win there.

“Because it’s on a baseball field,” answered Shelby Harris.

Harris played preseason games there during his first three seasons when he was trying to find a role with the Raiders. He learned then that “hand in the dirt” for defensive linemen isn’t just a metaphor.

“You’ve just got to really keep your feet under you, because you’re sliding a lot,” he said. “It’s tough. I just remember playing there my rookie year, my first two years there. You have no traction. You’re just sliding all over the place. You’re trying to take on a double-team, and you’re sliding 10 yards back.

“And it’s not like you’re doing something wrong. That’s just what it is.”

It’s also the way the game always was.

A BLAST FROM THE PAST

“Man, I still don’t get it — and I keep saying this over and over again. How does a pro football team play on a baseball field?” Harris said. “I don’t understand who thought that was a great idea — ever.”

“But it still blows my mind to this day.”

It wasn’t a great idea. It was a necessary one.

Seeing the lines of a football field painted over the infield dirt a throwback to a quainter time, when the money was smaller and a venue exclusive to an NFL team was not financially feasible.

Seventy-five percent of the league’s teams shared a stadium with a Major League Baseball team at one point in their histories. The Broncos are among them; they shared Mile High Stadium with the Colorado Rockies during their first two seasons, 1993 and 1994.

But for the 33 seasons prior to that, they shared the venue with Denver’s minor-league baseball teams, the Bears and the Zephyrs. And Mile High was a baseball stadium first, known as Bears Stadium before the expansions of the 1960s and 1970s turned it into a 76,273-seat colossus.

In 1981, 17 teams shared their stadiums with major- or minor-league baseball teams. Eleven of them had grass fields with full dirt infields. In those days, the clouds of dust you’ll see from midfield Monday in Oakland were a common early-season sight.

By 1991, the number was down to 13. A decade later, that tally was down to the Raiders and Dolphins, as teams like the Chargers and Vikings had watched while their baseball brethren left for gleaming, downtown, faux-retro baseball parks.

Since 2012, the Raiders have stood alone, kicking up the dirt. It hasn’t helped them much; they’re 5-7 in September home games in that span, compared with 19-21 in all other months.

FOR MANY BRONCOS, IT’S THE FIRST TIME ON DIRT

And unlike the tagline for the Durham Bulls in Bull Durham, no one will be calling this “the greatest show on dirt.”

The Broncos haven’t played a game on a field set up for baseball since defeating the Raiders 23-3 in Oakland three weeks into the 2009 season. None of their current players were with the team then.

“No idea,” defensive end Adam Gotsis said when asked how he would deal with it. “I haven’t played on it. That field is pretty chopped up regardless of when you play on it.”

Carr’s advice?

“If this is going out to to the Broncos, make sure you just wear tennis shoes,” Carr joked to Denver-area media. “The dirt is just fine. You won’t slip at all.”

In all seriousness, Carr acknowledged the differences.

“It is an adjustment,” Carr said. “You’ll see guys before the game if they’ve never played on it — especially the rookies and young guys — they all get out there on the dirt, and they’re trying to run and cut on it, trying to know what cleats they want to wear and things like that.”

But after the kickoff, other priorities take center stage. You might slip in the dirt, but the threat of being clobbered by an opponent or being tied up in a scrum drops the concern about the field down the priority list.

“When the game starts, to be completely honest, I don’t think about it,” Carr said. “I don’t think anyone does.”

Added Gotsis: “As they have to play on it, so do we. “You just hope you don’t get caught too much in that area, sliding around on that stuff.”

After Monday night, it will never be an issue for the Broncos again. Six days later, this part of NFL life will die, likely never to be resurrected.

Farewell, NFL games played on baseball fields. You won’t be missed.