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The Indianapolis Colts spent big money to protect their franchise quarterback.

So when Buffalo's Mario Williams got a clean shot on Andrew Luck on the fifth pass play of the preseason, left tackle Anthony Castonzo, like just about everyone else, was upset.

"He said, 'Do you want to get hurt, Andrew?'" Luck said, explaining the blown block was the result of a cadence error. "So I told him I'd publicly take that one on me. He's in the clear for that."

Assessing blame isn't the key issue in Indy's locker room. Keeping Luck upright is, which is why the Colts made an enormous effort trying to revamp their offensive line.

After watching the new franchise quarterback go down 41 times last season and get hit dozens more times, team owner Jim Irsay, general manager Ryan Grigson and coach Chuck Pagano all came to the same conclusion: take better care of Luck.

Grigson, a former offensive lineman who seemingly has a cellphone glued to his ear, wasted no time getting to work.

His first move in free agency was signing 314-pound Gosder Cherilus, a tackle from Detroit who could reinforce the right side. A few hours later, he added former New England guard Donald Thomas, a 306-pound sometimes starter who could help inside. Six weeks later, Grigson used a third-round draft pick on guard Hugh Thornton and a fourth-rounder on center Khaled Holmes.

So far the results have been mixed.

Though Luck wasn't sacked in Sunday's 20-12 victory over the New York Giants, he was knocked to the ground several times, and once scrambled for a first down. Backups Matt Hasselbeck and Chandler Harnish have been under duress in both games, too.

"We're a work in progress. It's going to take more practice, more games, but we're moving in the right direction," Thomas said Tuesday. "You always want to protect the quarterback. It's a pride thing."

But fixing an offensive line takes time and patience, things the Colts and Colts fans don't have much of.

On Saturday, Indianapolis (1-1) will host Cleveland in the third preseason game, likely the longest and last real test for the starting linemen before the Sept. 8 season opener against Oakland. And if they're going to keep Luck out of peril when the games count, the Colts need steady improvement.

"We made a big jump from the first game to the second game (of the preseason)," Castonzo said. "It just comes down to each guy getting the job done, and I think we'll be ready for the opener."

Perhaps nobody in the complex understands the potential consequences of failure better than Castonzo. When Indy took the Boston College alum in the first round of the 2011 draft, Castonzo thought he was walking into the most thankless job in football: protecting Peyton Manning's blind side. But Manning never played a down that season after having neck surgery, Kerry Collins sustained a concussion in Week 3 and never played again, and Indy wound up 2-14. The result: the No. 1 draft pick, a released Manning and a rebuilt roster with Luck as the centerpiece.

"They're improving every day. They were better this past week than they were the first week, and we feel really good about the first unit," Pagano said. "It's starting to shake out in the six, seven, eight and nine spots, too."

What they don't know yet is how Thornton and Holmes fit in.

While Cherilus and Thomas were solid throughout training camp and have played well in both preseason games, Thornton and Holmes have barely been on the field because of sprained right ankles. Pagano said Thornton could return this week, for the first time in nearly a month, and that he is a little ahead of Holmes, who was injured on the fourth day of training camp.

But there's another way the Colts can improve — with Luck's blocking calls.

"I think understanding protection is a big part of it, knowing who is going to be blocked, who are the free rushers, knowing when to get the ball out of your hand, knowing when to tell your running back, 'Maybe stay in on this one. I don't need you out on the route,'" Luck said. "Or making sure the running back does get on the route so you have that option. It's understanding protection and offenses and defense."

Ultimately, of course, it comes down to protecting Luck.

"I'd say we're on the upswing," Castonzo said. "We need to continue to improve, but we're coming together and we keep improving."

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AP NFL website: http://www.pro32.ap.org/poll