ENGLEWOOD — Ronald Fields is a big man and wouldn’t be nose tackle for the Denver Broncos if not for his massive girth.

But Fields’ survival in the middle is based on anticipation and intelligence as much as strength.

“It’s not easy,” Fields said. “You have to be able to read it fast. Read your keys, read the splits (between offensive linemen), learn the backfield sets — things that will give you an edge so you can anticipate what play you’re going to get.”

Fields, who is listed at 314 pounds, was signed in the offseason from San Francisco. He will start at nose tackle, and undrafted rookie Chris Baker is his backup. So far, coach Josh McDaniels has been happy with the progress of his nose tackles.

“You need to be on your toes, you need to be physical and you need to be able to play blocking schemes,” McDaniels said. “They work on it every day.”

At the snap, if the play doesn’t call for Fields to slant one way or another, he has to mirror the center, stepping where he steps. That requires quick reaction. Then Fields goes on to read the guards, who usually tip off where the play is going.

He has to either hold the middle against the run or get up field to create pressure on the quarterback. His play will be integral for the defense.

“The 3-4 defense, the nose is kind of the key to it,” Fields said. “If you can’t stop the run or push the pocket, your defense won’t be too good.”