ENGLEWOOD, Colo. -- If you listen to how things are going for the Denver Broncos these days, it might seem like Phillip Lindsay's full name is "And-Lindsay-wasn't-even-invited-to-the-combine."

Because that's often what folks end say about the rookie running back as he rockets through a sliver of space for yet another double-digit gain. Lindsay leads the Broncos in rushing yards, carries, rushing touchdowns and surprised looks.

As analyst Tony Romo said this past Sunday during the Broncos' 24-17 victory over the Pittsburgh Steelers: "The whole league made a mistake."

That's because Lindsay is the latest in a growing group of undrafted rookies the Broncos have signed, sealed and watched deliver. At 5-foot-8, 190-pound, Lindsay play with quickness, run with power and be mentally ready to perform in the biggest moments.

"I was surprised when I didn't get drafted when it happened, a little bit mad, just surprised," said Lindsay, who played at Colorado. "But since then, my focus has really just been on doing my job, being prepared to play and taking advantage every single opportunity. Because I always believe in my abilities."

Broncos linebacker Von Miller has been impressed with Lindsay's mettle.

"Phillip? Phillip is that same guy he was when he came in," Miller said. "I think Phillip believed he could play and what he could do, and he just comes in, gets to work and does it."

In 14 of the past 15 seasons, the Broncos have had at least one undrafted rookie make the team's opening week roster. Since 1997, 22 undrafted rookies have made Denver's opening week roster.

And the profile, according to two of the most decorated undrafted players in franchise history -- former wide receiver Rod Smith and current cornerback Chris Harris Jr. -- starts with confidence. It's the belief you were overlooked and far from unqualified.

"You work harder than you ever have before, as hard as you worked to get there, you work twice as hard to make it so you can stay," Smith said.

Harris added: "You have to believe you can make plays, and every day you try to make enough plays no matter what you're doing so they notice. When I was on special teams as a rookie, I went at it like I wanted to be the best gunner on punt team anywhere. When I played on defense, I wanted to be making plays no matter what."

In some ways it's also a product of the modern draft, which is just seven rounds. After the seven rounds are complete, there are many players remaining on draft boards around the league who carry a draftable grade and have futures as pros.

Among the players in the Broncos Ring of Fame, for example, Karl Mecklenburg was a 12th-round pick in the 1983 draft, the 310th player chosen the same year the Broncos traded for John Elway while Gene Mingo and Smith were undrafted players.

"Sometimes it's just how the picks fell that day," said Elway, the Broncos president of football operations/general manager. "Sometimes it's the picks that went in front of you, the names you have on the board when your picks came up and what you wanted to do in that moment. We know there are good football players left, players who could be really good Denver Broncos if we find the right guys and develop them."

In Mike Shanahan's last year coaching the team, two of the players who made the 2008 Broncos as undrafted rookies -- linebacker Wesley Woodyard and punter Brett Kern -- are still in the league with the Tennessee Titans. A third undrafted player in that class -- tackle Tyler Polumbus -- is now the sideline analyst for the Broncos' radio broadcasts.

"You kind of know the history here," Harris said. "You could see it again in camp, man, Phillip came to play. He's like me: He should have been drafted, but he wasn't. So you just show out every day to let people know."

Lindsay went from potential depth player and returner to potential runner in the backfield rotation to the current No. 1 option. The Broncos have tried to manage his workload, even in the two games that fellow rookie Royce Freeman missed with an ankle injury.

Lindsay hasn't had more than 18 carries in any game this season, but he has had two 100-yard rushing games -- he was the first back of the season to top 100 yards against the Steelers -- and four games with at least 90 yards rushing. Toss in his 24 receptions and you have a linchpin player in the offense.

When Broncos coach Vance Joseph was asked this week to explain how Lindsay has been such an effective between-the-tackles runner, he could have been summing up Lindsay's launch up the depth chart.

"It's speed and it's courage," Joseph said. "You've got to have courage to run through darkness, and that's what it is inside. Honestly, it is. In this league, the holes open and close. He has the courage and the speed to run through darkness and to run through the smoke, so to speak. He's so fast through the hole that by the time the linebackers see him, he's so close to them it's hard for those guys to tackle him. He gets into the secondary really fast. I think it's a combination of speed and courage."