Grant Cohn: 49ers’ biggest concern is the offensive line

Forget Colin Kaepernick and his development. Forget Frank Gore and his old legs. Forget NaVorro Bowman and his busted knee. Forget all of those concerns. The biggest concern facing the 49ers is the offensive line, from center to right guard to right tackle.

Through the first three preseason games the 49ers have gained just 38 yards on 15 direct handoffs, running plays designed to go behind the right side of the starting O-line – 2.5 yards per carry. The Niners have gained 67 yards on 12 direct handoffs designed to go behind the left side of the starting O-line – 6.2 yards per carry.

The left side of the O-line is left tackle Joe Staley and left guard Mike Iupati, two of the best run blockers in football. The other three-fifths of the O-line are center Daniel Kilgore, right guard Joe Looney and right tackle Jonathan Martin, who generate no movement at the point of attack. They are three of the worst run blockers in football.

Kilgore, Looney and Martin are new to the starting lineup. Kilgore replaced Jonathan Goodwin who signed with the Saints this offseason. Looney replaced Alex Boone who is holding out for a new contract. Martin replaced Anthony Davis who had shoulder surgery in the offseason and has missed all three preseason games.

Before Kilgore, Looney and Martin became starters, the 49ers had one of the best run-blocking O-lines in football. Dominant run blocking is the foundation of the 49ers’ offense. Dominant run blocking makes the 49ers’ offense work – they run more than they pass and their passing game depends on play action. Last season Colin Kaepernick’s passer rating was 103 on play-action passes and 83 on non-play-action passes.

Forget Michael Crabtree, Anquan Boldin, Stevie Johnson and all the other wide receivers the 49ers have this season. Those players are the rumpus rooms in the 49ers’ offensive mansion. The offensive line is the foundation. If three-fifths of the foundation disappears, the mansion will crumble.

Think like an opposing defensive coordinator. Size up the 49ers’ offense. How can it hurt you? The only way it can gain yardage on the ground is behind Staley and Iupati. Kilgore, Looney and Martin struggle moving defenders one-on-one in the run game – you don’t need additional defensive support to handle those three weak links.

So you’ll slant your defense to the left side of the 49ers’ offense and gang up on Staley and Iupati. One small adjustment takes away the entire 49ers’ running game.

The 49ers can’t let that happen. The 49ers need reinforcements.

Right tackle Anthony Davis might be healthy enough to start Week 1. It is unclear if he will play this Thursday in the final preseason game against the Texans – he started practicing just last week. He was a decent run blocker last season and a great run blocker two seasons ago. How good is he now after missing the offseason?

The 49ers lost their reinforcement at center on Sunday. They drafted center Marcus Martin in the third round this year. He was supposed to be a powerful run blocker. But he dislocated a knee cap on Sunday and will miss about two months according to the Sacramento Bee. So the 49ers have to live with Kilgore for now.

The Niners might have to live with Looney, too. Last week, the 49ers offered Boone a contract that would have made him one of the 12 highest-paid guards and, according to NFL.com, Boone turned down the offer. The 12th-highest paid guard will earn $6 million this season. Boone must realize how much leverage he has now that the whole world knows Looney can’t move anyone at the point of attack.

The 49ers’ running game can work around one weak run-blocker – Kilgore won’t kill the entire offense by himself. But the 49ers can’t work around two weak links side-by-side on the line. The Kilgore-Looney tandem won’t work. The 49ers absolutely need Boone back. They can’t afford not to pay him what he wants.

If the 49ers pay Boone and if Davis proves he’s healthy, the 49ers will have four-fifths of their foundation and the offense will be fine. Without those two, it could all come tumbling down.

Grant Cohn writes sports columns and the “Inside the 49ers” blog for The Press Democrat’s website. You can reach him at grantcohn@gmail.com.