TUCSON, Ariz. (AP) -- The spread offense has an image problem.
The perception of the spread is that it's a wide-open offense with receivers zigzagging across the field and a mobile quarterback who throws on every down or can take off when no one's open.
The reality of the spread is that it's often a run-first system and the cog that makes it go is an explosive, versatile running back.
''It really is a bit of a misconception,'' Arizona associate head coach and co-offensive coordinator Calvin Magee said. ''It (the spread) really is to take advantage of numbers, take advantage of angles, take advantage of the field. We still want to run the ball.''
The proliferation of spread offenses in college football has led to prolific numbers in recent years, teams piling up yards and points as defenses have tried to figure out ways to slow them down.
The idea of the spread is to make the defense cover all of the 53 1-3 yards between the sidelines and the 100 yards between the end zones.
With four and sometimes five receivers spread out across the line of scrimmage, there are more passing options and a natural inclination to believe that's what teams are going to do every time.
Many times, the passing game is just there to take the pressure off the run; some of the best spread offenses in the country run more than they pass.
Second-ranked Oregon, the standard-bearer for fast-paced, spread offenses, was a run-first team under Chip Kelly and that hasn't changed in its first season under Mark Helfrich. The Ducks have the nation's No. 2 offense overall and are No. 2 in rushing offense at 332.4 yards per game.
Northern Illinois has the nation's seventh-best offense and does most of its damage on the ground, averaging over 304 yards rushing, fourth nationally. Ohio State is a power-running team out of the spread, averaging nearly 280 yards per game, and Auburn churns out 300 yards per game rushing in a run-to-open-up-the-pass spread.
No. 6 Baylor has taken spread to a new dimension.
The Bears have had three different 1,000-yard rushers the past three seasons after having six total since 1945 and though they have more passing yards than rushing, still like to run first. Baylor leads the nation in total yards with 714 per game and is seventh nationally in run offense at 300 yards per game.
''I grew up with a run-based offense, so we're always going to run the football,'' Baylor coach Art Briles said. ''We'll throw it for flair, but we're going to run it to win.''
The teams that run the spread the best have one key element: A great running back.
Arizona runs one of the fastest spread offenses in the country under coach Rich Rodriguez and it's keyed by Ka'Deem Carey, who's leading the nation in yards per game for the second straight year, averaging 160 yards this season.
Baylor's versatile Lache Seastrunk is ninth nationally at 126 yards per game, while Oregon always seems to have someone among the rushing leaders, including Byron Marshall at No. 20 this season.
Washington turned to an up-tempo, spread offense this season and it's worked because of Bishop Sankey, who was the nation's leading rusher until Arizona State bottled him up last weekend.
''I think just the running game in general is huge, for us,'' Washington coach Steve Sarkisian said. ''I don't know how everyone else operates, but for us so much of what we do comes off of our running game. We're just fortunate we have a guy in Bishop that can handle that load.''
Part of what makes running teams so effective out of the spread is the formation creates more running lanes. With so many players spread out trying to cover the receivers out by the sidelines, it forces teams to make up more ground to clog holes that backs might run through.
Many of the teams that run the spread have similar plays to offenses that run out of the I and other formations, it's just that the running backs usually come from the side of the quarterback instead of directly behind.
The key to making it work is finding a versatile running back who has good quickness, is explosive through the hole and runs hard - essentially all the attributes any good running back in any system should have.
''If you don't have a good running back in a so-called pro-style offense, it makes you one-dimensional as well,'' Magee said. ''You want to have a good tailback because you want to be able to take advantage of those lanes you are creating with those matchups.''
As some of the nation's offenses have shown, it works.
AP Sports Writers Stephen Hawkins in Dallas and Tim Booth in Seattle contributed to this report.