WESTFIELD, Ind. — Quarterback Justin Fields won’t play Saturday night when the Chicago Bears meet the Indianapolis Colts at Lucas Oil Stadium (6 p.m., Fox-32). Most of the Bears starters won’t. That was the decision coach Matt Eberflus came to this week, concluding that the two crossover practices the Bears held with the Colts provided a properly competitive workload that tested and pushed the starters.

But the game must go on. And the Bears will open the door Saturday evening to players fighting for roles or roster spots. Here are four things to watch.

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Sure, with Fields out, P.J. Walker will likely get the start. And his progress and production certainly is notable as the Bears assess what they have behind Fields in case of an emergency during the regular season. Nathan Peterman also should log time under center Saturday.

But August games are often about the underdogs. The big underdogs. And through that lens, Tyson Bagent should remain a fun watch this weekend. The undrafted rookie from Division II Shepherd University has been an intriguing contributor inside the quarterbacks room since May.

Bagent threw for 17,034 yards and 159 touchdowns during 53 games at Shepherd, including a school-record 518 yards against Notre Dame College in 2018. Bagent’s first preseason action against the Tennessee Titans last week wasn’t quite as prolific. But it was solid. He completed 4 of 5 passes for 37 yards, including a 25-yard connection to Daurice Fountain on fourth-and-7 that kept the Bears’ final scoring drive alive.

Over the next eight days, Bagent will have his opportunities to state a case for a practice-squad job. His performances should be fun to watch.

Tremaine Edmunds has gone almost three weeks since he last practiced, still sidelined with an undisclosed injury. Fellow starter T.J. Edwards is likely to get Saturday night off as well. If Jack Sanborn plays, it shouldn’t be more than a series or two.

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That will leave the door open for a horde of other linebackers to step forward and make plays. Fifth-round pick Noah Sewell should grab some of that spotlight. Veteran Dylan Cole, who is also a key special teams contributor, could see early work as well. Don’t forget undrafted rookie Micah Baskerville, who has shown his playmaking ability in practices the last few weeks.

The Bears also have been active with their roster churn at the position, claiming fourth-year vet Mykal Walker off waivers this week and adding Davion Taylor to the 90-man roster Thursday. (The Philadelphia Eagles cut Taylor on Aug. 6.) Barrington Wade, once a star at Niles North High School, also has been with the Bears for the last two weeks.

The search for depth is always ongoing, and preseason action is a great test.

Pettis spent more than two weeks on the non-football injury list at the start of training camp and has been back on the field for only five practices. But there’s an opening for him to remain part of this receiving corps for the season, particularly after Velus Jones Jr. fumbled during a punt return against the Titans last weekend. Jones also missed Thursday night’s practice with an undisclosed injury and seems unlikely to play Saturday.

Pettis had 19 catches, 245 yards and three touchdowns last season and proved to be a reliable punt returner. That’s his specialty as he looks to grab a spot on the 53-man roster as part of a position group at which he undoubtedly will slot behind DJ Moore, Darnell Mooney, Chase Claypool and Tyler Scott.

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None of those players figures to suit up Saturday, which will leave the pass-catching duties up to Pettis, Equanimeous St. Brown, Fountain, Nsimba Webster, Isaiah Ford and Joe Reed.

The preseason is always a good trial run for NFL staffs to iron out their processes. That means crisp communication between the coordinators and head coach within the game. It means running through replay-challenge procedures efficiently. It means practicing clock management and situational awareness.

Even with most of the starters sitting out, Matt Eberflus will need to remain dialed in and sharp. He also will have to show some skill as a motivator and spent parts of the last three days reminding the reserves of the opportunity that the game presents.

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To his full team, Eberflus has continued to emphasize that the Bears are far from meeting his standards in terms of their attention to detail in all phases.

“It needs to be tighter. It needs to be more efficient,” Eberflus said Thursday night. T”he detail needs to be there. Precision and detail matter. Because then you know what to do and how to do it and you can play with speed. That’s how you win downs. And that’s how you win football games.”