By Chris Emma–

LAKE FOREST, Ill. (CBS) — Every NFL player at some point in his rookie season has that eye-opening moment in which he learns the hard lesson of the vast size and speed of this league.

Bears center Hroniss Grasu’s moment came just minutes into his first NFL start. With the Bears backed to their own end zone, Chiefs 301-pound defensive lineman Jaye Howard bull-rushed through Grasu, then defensive end Allen Bailey followed. The two Chiefs took quarterback Jay Cutler down for a sack-strip touchdown and treated Grasu like a turnstyle.

Welcome to the NFL, rookie.

Early into their 2015, the Bears faced a challenge when center Will Montgomery suffered a season-ending knee injury in their fourth game. The Bears had hoped Grasu wouldn’t need to take the field as a rookie, with a source indicating 2015 was supposed to serve as a “redshirt” year. One game after Montgomery went down, Grasu was starting against Howard, Dontari Poe and the Chiefs.

Grasu had many moments like that double-barreled bull rush that he simply couldn’t handle. It wasn’t only the fact that Grasu — now 310 pounds in his second season — was then undersized, but he was hesitating. He was wasting precious milliseconds thinking.

“It’s crazy, the speed’s so fast in this league where you can’t get caught thinking,” Grasu said in an interview at the Bears’ OTAs last week. “You got to just go, you got to just play, and you got to make the right all right away.”

A 24-year-old 2015 third-round pick out of Oregon, Grasu is positioned to be the Bears’ starting center this season — and they hope for years to come. The key this offseason was for Grasu to put in time bulking up, and that added size appears to be paying dividends in camp.

However, the size alone wasn’t Grasu’s greatest issue. He had to gain enough of a grasp for his duties at center to where he could read and react seamlessly. Grasu entered this offseason with a goal.

“Find one thing a week in the playbook to get better at,” Grasu said. “Find one thing to master, and then move onto the next thing. I was doing that all offseason, and it’s really been paying off so far in OTAs.

“If you don’t know what you’re doing, if you’re thinking too much, it doesn’t matter how strong or fast you are, that split second that you’re thinking, you’re going to get beat. Not having that second to think anymore, to go and play fast, it’s been making a difference in my play so far.”

Grasu now feels more comfortable and confident, and it reflects in his play. He’s now instant off the snap and has a good feel for where to go. Bears offensive line coach Dave Magazu played a role in helping grow Grasu into a steady presence for the unit, but there were plenty of influences, too.

Words from Bears quarterback Jay Cutler still stand out to Grasu. When he was struggling, they went a long way.

“(Cutler) told me he believes in me and this team believes in me,” Grasu said. “When a guy like that, it shows he has confidence in me.

“I’ll do whatever it takes to help Jay. I’ll lay my body on the line for that man.”

A native of Los Angeles, Grasu brings a bit of California cool with his personality off the field, but he can flip the switch in the huddle. The soft-spoken guy is adapting to a role requirement at center, which is being vocal.

Bears teammates have seen a different side of Grasu during OTAs.

“Seeing him be a leader now is just great,” Bears tackle Charles Leno said.

The Bears made moves to their offensive line, moving Pro Bowler Kyle Long back to his more natural position of right guard and signing Bobby Massie to handle right tackle. They can hope for second-round pick Cody Whitehair to fit at left guard but also signed Ted Larsen and Manny Ramirez for depth. Leno returns to his spot at left tackle.

Entering this offseason, Grasu was arguably the biggest question mark for the Bears offensive line. He’s working to be a stabilizing force.

Now fit to handle his role better than last year, Grasu believes he’ll be ready when some of the game’s best comes on a bull rush, as he strives to keep improving more and more.

“I’m always open for anything, whatever it takes to get better, and there’s a lot I need to get better at,” he said. “It’s going to be a good year.”

Chris Emma covers the Bears, Chicago’s sports scene and more for CBSChicago.com. Follow him on Twitter @CEmma670 and like his Facebook page.