What are Bears looking for from Fields in Saturday's preseason finale?

Justin Fields will trot onto the field Saturday at Nissan Stadium in Nashville, Tennessee, to start preseason game No. 3 for the Bears. After Saturday, it's anybody's guess when the rookie will start another game.

Bears head coach Matt Nagy has been adamant that 11th-year veteran Andy Dalton is the team's starting quarterback. Dalton will start in Week 1 against the Los Angeles Rams on Sept. 12.

Opinions vary widely on when Fields will make his first start in the regular season. The only opinions that really matter, though, are those coming from inside Halas Hall. Those are the opinions of Nagy and his coaching staff, as well as the opinions of general manager Ryan Pace and his staff.

Performance is going to matter. That was probably a safe assumption previously, but Nagy made that clear this week.

"Big picture, when we talked about this from the very start, we said whoever is going to be best for the Chicago Bears and that's going to obviously deal with production and wins, right?" Nagy said. "So when you look at this thing, you want to make sure we all support each other with one common goal to win and, offensively, to score touchdowns."

So what exactly is Fields trying to accomplish in these preseason games? He isn't going to win or lose the starting quarterback job Saturday.

According to his coaches, this is all about simulating the feel of a regular week in the NFL. It's also about giving him a chance to feel uncomfortable. That's going to continue into the regular season, too.

"Get in a routine and then be ready to get uncomfortable on a Thursday night game," quarterbacks coach John DeFilippo said. "Be ready to make sure you don't overanalyze things on a Monday night game when you have extra time. Those are learning experiences. I can help a player so much, but he has to go through these things."

Everything about life in the NFL is new for Fields. That applies to the practice field, game day, even life at home when he's off the clock.

Fields spent a good portion of this summer working on his cadence. In effect, working on listening to the play call in his in-helmet headset, and regurgitating it in the huddle. It sounds like a little thing, but it takes time for rookie quarterbacks to get down. Most college quarterbacks aren't calling plays in the huddle.

But there are countless more examples of little things that are different. When Fields played in his first preseason game two weeks ago, it was the first time he heard the play call in his helmet headset. It was the first time he went to the sideline and analyzed still photos from the game on a tablet as the game was going on. It was the first time he spoke with his coaches upstairs in the press box via the sideline headset.

All of this is new, on top of the fact that he's learning a new playbook and playing against defenders who are the most elite in the world.

Offensive coordinator Bill Lazor said the team will use those still photos to analyze what looks the defense showed vs. what it actually did once the ball was snapped. College football still doesn't allow the use of tablets on a team's sideline. The NFL allows it only for still photos, not film.

"It's a big change," Lazor said. "If you use those pictures it really allows you to be coached and to work together and to advance and make adjustments in games."

Lazor knows how hard Fields is working at it. He has received enough texts in the evening from the rookie quarterback to know that he's not wasting his time at home.

"Not too late," Lazor said. "He's respectful."

Everybody at Halas Hall raves about Fields' work ethic. DeFilippo believes it's the sign of a quarterback who has bought in. One day last week, Fields asked DeFilippo to go through the tape from an entire practice one extra time.

Fields is focused on the details. It's not flashy and it doesn't make the highlight reel, but little things like that make a difference for a young quarterback.

"The intricacies and the plays and repping every play and getting it down," Fields said when asked what his focus is right now. "Just getting reps after reps after reps. But the thing in the huddle and stuff like that, I feel comfortable with that now, so now it's focusing on the little things now that I have a base under me."

Fields is sitting behind a veteran who has been there, done that. Two weeks ago, it was a surprise when Dalton made one mental mistake, forgetting to send a player in motion during practice. For Fields, this is the time to make mental mistakes.

He's going to see an entire half of football Saturday. Yes, the Bears want to see him slinging the ball deep down field, and yes, they want to see him take off and run for first downs.

But the way he handles himself in the huddle, and the way he handles his business on the sideline between drives, those are the things that will tell Nagy, Lazor and DeFilippo when Fields is ready to play in a real game.