At the same time, opponents can switch up coverages and blitzes, hoping to force a mistake. When a quarterback makes a mistake, it can be costly. “It’s the most important position, that quarterback position,” said Stanford coach Jim Harbaugh, a former star quarterback at Michigan. “You spend a lot of time training that guy. Keeping him healthy, putting him in a position to be successful and make plays for your offensive unit, all those things are critical. That’s a guy you don’t want to lose.” The Ducks have a capable backup, Brady Leaf, the brother of Ryan Leaf. But it’s hard to imagine they’d be contending for a national title without Dennis Dixon, a fleet-footed senior who has emerged as a Heisman Trophy contender. Dixon leads the conference in passing efficiency and is sixth in the country. Dixon has 16 touchdown passes and only three interceptions in 224 pass attempts. Carpenter, a junior, is second to Dixon in Pac-10 passing efficiency. He has thrown 17 touchdown passes against seven interceptions. If Carpenter can’t play Saturday, the Sun Devils will turn to sophomore Danny Sullivan, who has completed 11 of 14 passes for 91 yards and a touchdown in mop-up duty. “When you start getting into changing quarterbacks, it becomes – I don’t want to say a problem, but there’s just not the continuity when you have that guy that’s been there every day and has been your experienced leader,” Cal coach Jeff Tedford said. Just ask the Trojans, Golden Bears and Bruins. All three teams have had their seasons rocked by quarterback injuries. USC’s John David Booty, a fifth-year senior, had been playing inconsistently before he got hurt. But Booty’s season took a sharp turn down when he broke his finger in the second quarter of USC’s 24-23 loss to Stanford on Oct. 6. He threw four interceptions in the second half as the Cardinal stunned the Trojans. Booty has missed USC’s last three games. His replacement, third-year sophomore Mark Sanchez, has played capably at times, but he threw two interceptions in a 24-17 loss at Oregon last week. Booty practiced with the first team this week and could be back when the Trojans (6-2, 3-2) play Oregon State on Saturday in the Coliseum. “Very rarely are teams dominant enough that they can maintain the same level of play,” USC coach Pete Carroll said. “It doesn’t mean you can’t win. But it’s hard to maintain the same level of play, or the other guy would have been the starting quarterback.” California (5-3, 2-3) rose to No. 2 the week after an emotional victory at Oregon on Sept. 29. But starting quarterback Nate Longshore sprained his ankle in that game, and Cal hasn’t won since. Longshore didn’t play in a 31-28 loss to Oregon State. The upset ended when his replacement, Kevin Riley, was tackled short of the goal line on the game’s final play, costing the Bears a chance to send the game into overtime. Longshore, still hobbling from the injury, has played in the last two games. Longshore has thrown five interceptions in those losses. UCLA (5-3, 4-1) was down to third-string quarterback McLeod Bethel-Thompson for most of a 20-6 loss to Notre Dame on Oct. 6 after starter Ben Olson went out with a knee injury; Patrick Cowan was sidelined already with a knee injury. Bethel-Thompson threw four interceptions against the Fighting Irish and lost a fumble that was returned for a touchdown. Cowan helped lead UCLA past California on Oct. 20 but was ineffective in a loss to last-place Washington State last week. The Ducks and the Sun Devils have yet to lose a game because of a quarterback injury. But ASU’s luck may have taken a turn last week, when Carpenter sprained his thumb handing off to tailback Keegan Herring in a 31-20 victory over Cal. “Quarterbacks always have a tough time staying healthy because teams really want to try and get after the quarterback and get as many hits on that person as they can,” Carpenter said. “I think for Dennis Dixon and I, we’ve been very fortunate to have a good offensive line protecting us and giving us a chance to stay healthy. “I think it also has to do with a little bit of luck as well.”160Want local news?Sign up for the Localist and stay informed Something went wrong. Please try again.subscribeCongratulations! You’re all set! AD Quality Auto 360p 720p 1080p Top articles1/5READ MOREGame Center: Chargers at Kansas City Chiefs, Sunday, 10 a.m.It’s turned into the Year of the Depth Chart. Injuries to starting quarterbacks at USC, California and UCLA have produced disastrous results. Meanwhile, No. 4 Oregon and sixth-ranked Arizona State have kept their quarterbacks healthy – so far – and that’s a big reason they’ve emerged from a jumbled race. It’s uncertain whether ASU’s starting quarterback, Rudy Carpenter, will be healthy enough to play Saturday. Carpenter sprained the thumb on his throwing hand last week, but Coach Dennis Erickson said Carpenter will play when the Sun Devils (8-0, 5-0 Pac-10) and Ducks (7-1, 4-1) meet in Eugene in the West Coast’s most anticipated game of the season. “Quarterback is huge that you stay healthy, because he’s the guy that runs the show,” Erickson said. “You better have a couple guys, but if you keep your first quarterback healthy, it makes a heck of a difference.” When a starting quarterback gets hurt, it can affect the entire offense. Receivers have to develop timing with a new thrower. Linemen have to learn whether the replacement will stay in the pocket or take off at the first sign of pressure. COLLEGE FOOTBALL: Teams are hurt from the loss of their top quarterbacks. By Andrew Bagnato The Associated Press TEMPE, Ariz. – With eight of the top nine passers from last season returning, this was supposed to be the Year of the Quarterback in the Pacific-10 Conference.