The Brown's offensive linemen don't wear dorky glasses taped in the middle or pocket protectors. They do protect the pocket, though.

Cleveland's line, a collection of five book-smart, weight-trained athletes anchored by a Pro Bowl center who graduated from California-Berkeley and keeps "The Thinker's Thesaurus" handy for reference in his locker, has paved the way to the Browns' solid start.

They're the brains and brawn of the Browns.

"Just stand near them and listen to them to talk," said first-year coach Mike Pettine. "They're football nerds. That's all they talk about is football. They get into some real in-depth conversations about it, and it shows on the field. They work very well together. It's a very intelligent group, and I think they're very well suited for the scheme."

The scheme.

Under new offensive coordinator Kyle Shanahan, the Browns switched to a zone-blocking scheme this season. It can be a complicated system to learn with many details and nuances. Pettine and his staff knew it would take time for the Browns offensive line to become comfortable with something so foreign.

They expected a steep learning curve. This group, though, flattened it quickly.

Pettine said he didn't expect the line to come so far this quickly.

"But when you look at the group and just how smart they are and how hard they work and the way they get coached, looking back on it, it's not a huge surprise," Pettine said. "It is safe to say that they're further ahead of where we thought they would be."

Through four games, Cleveland has the fourth-ranked rushing offense and the Browns already have more rushing touchdowns (5) than they had all last season (4). The offensive line — Mack, Pro Bowl left tackle Joe Thomas, rookie left guard Joel Bitonio, right guard John Greco and right tackle Mitchell Schwartz — has allowed just five sacks, giving quarterback Brian Hoyer time to make plays and keeping him healthy.

According to profootballfocus.com, Cleveland has the league's top-rated offensive line.

"It's good to hear that stuff," said Schwartz, another Cal grad. "But I don't look at it too much. It's pretty hard to figure out the grading for us. It's obviously cool we're up there, but sometimes we don't know if we're getting a plus or minus ourselves. Those sites do a really good job but it's hard to evaluate or put a quantitative grade on it. That being said, it's very cool."

Schwartz is the one lineman with a nickname: "The Oracle."

"He sees all and he knows all," joked Greco, who switched to right guard after starting 13 games at left last season. "He's never wrong and even when he is, he'll convince you he's right."

True to his well-read reputation, Schwartz sat at his locker following Thursday's practice in front of an open laptop computer while working on a crossword puzzle. Schwartz was a bit of a puzzle last season, when his play was harshly criticized. But to this point in 2014, the soft-spoken, 6-foot-5, 320-pounder may be the team's most improved player.

Thomas didn't think his teammate played poorly. And just like he protects Hoyer's blindside, the perennial All-Pro had Schwartz's back.

"I felt a lot of the criticism he got was unfair," Thomas said. "Do we get beat at times? Yeah, everyone gets beat or gives up sacks or has bad plays. But for whatever reason since I've been here, it seems like the right tackle every year has been kind of like the fall man for whatever reason."

One of the main reasons for the success of the Browns' O-line has been continuity. Thomas (7,186), Mack (5,189) and Schwartz (2,353) have never missed a snap as pros. The group is also well-balanced with size on the ends, athletic guards and a burly center with a beautiful mind.

To Greco, Mack is the group's nerve center.

"He's one of the smartest football players I've ever been around," he said. "And when you have a guy like that who orchestrates everything and gets guys lined up, it's amazing how many wrinkles are ironed out that you take for granted. We've been spoiled around here because we have him."

"Alex is what makes our engine go," Greco said.

NOTES: Pro Bowl CB Joe Haden (hip) missed his second day of practice, increasing the chance he'll miss Sunday's game against the Steelers. If Haden's out, undrafted rookies K'Waun Williams and Robert Nelson could get extensive playing time. ... Starting LB Paul Kruger missed practice with a back injury.