The zone read has become one of the most popular offenses in college football, a multidimensional shotgun-based option system that requires impeccable timing and often leaves defenses guessing and grasping.

The innovation hatched from a mistake.

The year was 1991 and Rich Rodriguez, in his second season as Glenville State's coach, was searching for an offense that would keep defenses off-balance.

An inadvertent epiphany came during a practice when quarterback Jed Drenning bobbled a handoff, gathered himself and made a split-second decision to run after seeing the defensive end pinch inside.

"He said he saw the end coming in, kept it and ran for 15 or 20 yards. So I told him, 'yeah, we were going to put that in next week,'" Rodriguez said with a laugh. "Then I thought: We may be onto something here."

He sure was.

Rodriguez ran the offense in relative obscurity while at Glenville State, but started gaining attention for his innovative system when Tulane went 12-0 with quarterback Shaun King running the zone read. Once Rodriguez became the offensive coordinator at Clemson with quarterback-with-tailback skills Woody Dantzler, word was out.

As Rodriguez moved on to jobs at West Virginia, Michigan and now Arizona, the zone read spread across college football.

Now many of the most explosive offenses in the country are running the zone read or have a package of plays with it, including Oregon, Baylor, Texas A&M, Arizona, Auburn, Ohio State, Arizona State, Kansas State — and the list goes on and on.

"Any time anyone has success doing something, other teams will also try to do it," Auburn coach Gus Malzahn said. "That's kind of where the game is going right now with the quarterbacks who can successfully run a zone-read type concept."

At its genesis, the zone read was based on one read: The defensive end.

The quarterback lined up in the shotgun, took off left or right with the running back trailing, and made a judgment based on the defensive end's movement. The end stays wide or goes upfield, he hands off to the running back. The end pinches in, the quarterback keeps and runs outside.

But the offense has become far more complex since that first bobbled snap at Glenville State.

Now once the quarterback keeps the ball, a multitude of further reads and options follow.

He still has the option of running after getting around the end. But if the quarterback sees the linebackers move up to stop the run, he can lob a pass over their heads to the tight end. Pick up on the safeties coming up, he can throw downfield into one-on-one coverage. Catch the cornerback charging in, he can hit a receiver on a quick slant or bubble screen.

The reads aren't always the defensive end, either. Some teams key on the middle linebacker, the safeties, even the nose tackle.

A few even have pre-snap reads, basing play calls on where certain defensive players are lined up.

It's still option football, just out of the shotgun — which makes all the difference.

"When the quarterback hands the ball off after taking the snap under center, he's not really a run threat and you're basically playing 10 on 11," said Rodriguez, in his third season at Arizona. "Get into the shotgun, you can see the defense and hand the ball off. You're actually playing 11 on 11. You can get positive yards and make them play 11 on 11."

The zone read still has defenses backpedaling.

For years, defensive players were taught to read the offensive linemen to determine if it was a run play or a pass.

In the zone read, the quarterback has the option of throwing, so defenders now have to account for both. Guess wrong and they're scrambling to get back into the play.

The offense also is run out of the spread, which is designed to get playmakers into open spaces. With defenders inching up to account for the run, one missed tackle can turn into an 80-yard touchdown.

"When you get in the gun and are utilizing more receivers, spreading things out, it creates more space than the traditional triple option where there's 11 guys in a couple yards of space with each other," Arizona State offensive coordinator Mike Norvell said. "We're just taking the challenges that were presented then and spreading them out to make them defend the entire field."

The new breed of quarterbacks is making it tougher to stop.

The days of the drop-back passer are dwindling, replaced by athletic playmakers who can run or pass and make split-second decisions in the flick of a ball fake.

Baylor has set records with Bryce Petty under center. Oregon flies past opponents behind Marcus Mariota. Nick Marshall led Auburn to last season's national title game. Johnny Manziel won a Heisman Trophy at Texas A&M and Kenny Hill has picked up where he left off.

These guys are talented and now they're everywhere.

"I liked it when there were fewer people running it because it was easier to be unique," Rodriguez said. "Now it's hard to be unique anymore."

Teams are still finding ways — and it's still hard to stop.

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AP Sports Writer John Zenor in Birmingham, Alabama, contributed to this story.