By Ralph D. Russo AP College Football Writer

What started as a quirky twist on the shotgun formation by an off-the-radar team searching for an edge has become the hottest offensive trend in college football.

It's called the pistol, and if you haven't seen it, well, you're probably not paying close enough attention.

Invented in Nevada, the short shotgun setup — hence pistol — that places the quarterback about 4 yards behind center and a running back 3 yards behind the QB is being used in varying amounts at Alabama, Arkansas, Duke, Oklahoma, Oklahoma State and UCLA, just to name a few.

And the Michigan football team will face Indiana’s version of the pistol on Saturday (3:30 p.m., ESPNU).

But the pistol doesn't fire magic bullets.

Indiana began using it last season to boost its running game after it went from mobile quarterback Kellen Lewis running its spread offense to current starter, Ben Chappell, who is more of a dropback passer.

The Hoosiers rank last in the Big Ten in rushing this year and were among the worst last season, too. However, they are second in the conference in scoring at 41.3 points per game, a tick ahead of Michigan’s 41.2. Led by Chappell, Indiana has the No. 1 passing offense in the Big Ten, averaging 304.3 yards per game.

At UCLA, the Bruins have gone all in on the pistol, and last week they used it to whip Texas 34-12.

"It's expanded the offensive landscape," said Nevada coach Chris Ault, the pistol's founding father.

No team's pistol is more potent than the Wolf Pack's. Ault's team has put up dizzying numbers, averaging more than 500 yards and 37 points the previous two seasons, running a spread-option offense from the pistol. This year, with senior quarterback Colin Kaepernick pulling the trigger in Reno, Nevada is on the cusp of a breakthrough season.

The Wolf Pack is 4-0 for the first time since it moved into Division I-A in 1992, and at No. 25, is ranked in the AP Top 25 for the first time since 1948. That includes victories at home against California and at BYU.

And the pistol is pumping better than ever. Nevada is fourth in the nation in total offense, averaging 529 yards, and is the fifth highest scoring team in the country at 45 points per game.

Vai Taua is the Western Athletic Conference's leading rusher at 113.3 yards per game and Kaepernick is second at 112.8. The 6-foot-6 quarterback has improved as a passer, throwing for 924 yards to complement the Wolf Pack's deceptive and explosive running game.

Ault's brainchild has come a long way from the winter of 2005, when the coach who had built a Hall of Fame career on a pass-happy offense dubbed 'Air Wolf' decided he needed to come up with a better way to run the ball.

From the shotgun, Ault's preferred way of lining up, backs did too much running from side to side instead of moving straight forward and hitting the line of scrimmage with a head of steam.

So Ault decided to move the quarterback up a few yards and placed a tailback behind him, sort of combining an I formation and a spread.

"When I brought it to my staff they all looked cross-eyed at me," Ault said with a laugh in a recent telephone interview.

Ault and his staff drew up the offense, then installed it during spring practice.

"There were some ugly days," he said.

But the team was fully committed to the pistol.

"We just made a resolution that we would go through all spring doing that," said Arkansas offensive line coach Chris Klenakis, who was offensive coordinator at Nevada from 2004-09. "Footballs were flying everywhere; it was an experiment in progress. We went through it, but the best thing we did is we had the guts to stick with it because nobody had done it before. The next season, we won a championship and it's taken off from there."

There has been a steady stream of coaches showing up in Reno and dialing up Ault looking for advice ever since.

UCLA coach Rick Neuheisel came calling after last season.

"Most great ideas are born of necessity," he said. "We needed to run the football better. Looking at the equipment that we had with respect to personnel and what we were trying to get accomplished my first two years at UCLA, it just wasn't working. We had to accept that."

While Neuheisel said the Bruins still have a lot of learning to do, so far the change has to be rated a success.

UCLA (2-2) is third in the Pac-10 in rushing at 218 yards per game, and the Bruins hammered Texas for 264 yards in a 34-12 upset in Austin last week.

Teams such as Oklahoma, Alabama and Arkansas just dabble with the pistol formation.

"All we're doing when we put the guy in the pistol is we're putting our (running back) directly behind the guy instead of on the side," Sooners offensive coordinator Kevin Wilson said. "That's to hide a tendency you might have and that's to get your running back downhill instead of sideways so much.

"We're not running the zone-read options or the inside, mid-line veers or read options."

So what makes it tough to defend?

Texas Tech linebacker Bront Bird played at Nevada in 2008 and the Red Raiders won 35-19. He said the pistol causes problems for linebackers who try to decipher which way a play is going by watching the running back's first step.

"It just looks weird and there's just so many different things you can do" out of it, he said.

BYU coach Bronco Mendenhall's team gave up 24 points in the first half of its 27-13 loss to Nevada last week, then settled down in the second half when it became more familiar.

He said the pistol prevents defenses from overloading left or right, depending on which side of the quarterback the running back lines up.

"The capability to run basically an option-type of football and throw the football decently, those two things are what I think makes this particular scheme fairly difficult to defend," he said.

Those are words that make the 63-year-old Ault, who has 210 victories in 26 seasons at Nevada, smile. When it comes to the pistol, he's one proud papa.

"It's been a lot of fun," he said. "Every year you're adding to it, seeing where it can go next."