The trend remains hard to escape even for those with breathtaking speed. The NFL running back position has become a timeshare. In a pass-happy league, the average number of attempts per season for top-10 rushers continues to decline.

It sank to 280 last season. It sat at 284 in 2013. As recently as 2006, it was 338. Good teams run the ball, but the growing evidence raises the question: Are the days of the bell cow back over?

Not if Broncos coach Gary Kubiak has his way. While multiple backs offer versatility and protection for injury, a front man still can exist, if not prosper.

“I can tell you this, I believe in the (bell cow). And I believe it’s up to the player to prove he can do that. Do you need two guys in a season? You are darn right, in this league,” Kubiak said after practice Tuesday. “But I think if a guy goes out there and he shows he can play three downs, can protect the quarterback, and can handle it, then he should stay out there.”

The Broncos boast a stable of talented, young backs. C.J. Anderson leads the group, an undrafted free agent who turned opportunity last season into a Pro Bowl berth. Montee Ball lost the starter’s job because of ineffectiveness and multiple injuries (apendectomy and groin). Ronnie Hillman provides a slippery change of pace, and capitalized in a limited window last season before injuring his foot. Juwan Thompson brings an added dose of power, possessing fullback strength, but a tailback’s vision.

Four backs. One job. For now, it’s Anderson’s to lose.

“He has told us if you get the chance and play well, you will stay out there. My goal is to be out there all three downs,” Anderson said. “That’s my plan.”

Kubiak’s history with running backs provides a road map of his intentions. He rewarded those who performed. Five times his top running back finished in the top 10 in carries from 2006-to-2014, spanning his time as the Houston Texans’ head coach and the Baltimore Ravens’ offensive coordinator. Arian Foster led the league in 2012 with 351 and also finished in the top 10 in 2010 and 2011. Steve Slaton (2008) and Justin Forsett (2014) also cracked the the top 10 list.

Forsett shows Kubiak’s open mind to relying on a workhorse. Playing for his fifth team in seven years, Forsett filled the void left by Ray Rice’s termination, finishing 10th in the NFL with 235 attempts. And it wasn’t like he didn’t have a capable backup in Bernard Pierce.

“With Justin, he went in as a role player and all of sudden, it was like, ‘Why are we taking this guy off the field? He was doing everything we asked,” Kubiak said. “He earned the right to stay out there.”

Anderson reported to camp at 218 pounds, a lighter bowling ball equipped to go 10 frames, if you will. The zone-blocking scheme requires the back to put his foot in the ground and slice the field in half with a cut back. The Broncos ran inside zone plays last season, and are adding outside stretch calls.

“If we get the holes like they had in Houston, oh man,” Anderson said.

Evaulating with certainty begins with the preseason games because the Broncos, for obvious reasons, don’t cut block in practice.

“It’s a healthy competition,” said Ball, who is working on using feet better after contact. “I tell (Anderson), ‘Soon as you slip up I’m right there. And he knows it. That’s how he got his opportunity.”

Hillman doesn’t profile as an every down back. Still, he showed quickness and toughness with 100-yard games in victories over the Jets and Chargers last season.

“We all have ups and downs. Right now they are getting most of the reps. But it’s early in camp,” Hillman said. “We have a lot of preseason and season to go, so I am not worried about it.”

The popular football axiom goes: if you have two quarterbacks you have none. Kubiak posseses at least four running backs, but if the starter takes advantage, he will lean on one.

Troy E. Renck: trenck@denverpost.com or twitter.com/troyrenck