The Bears (2-1) host the Jets (1-2) at Soldier Field on Sunday at noon, and for the second straight week they will do it without Caleb Williams. As of Friday, Williams was ruled out with the Grade 2 hamstring strain he suffered against Minnesota on Sept. 20, and Ben Johnson was keeping his choice between Case Keenum and Tyson Bagent to himself until game day. Here is what the matchup comes down to.

The ground game is the constant

Whoever starts at quarterback, Chicago’s identity is already clear. Through three weeks the Bears lead the NFL in rushing at 184.3 yards per game and in yards per rush at 5.27. That second number matters most: it measures how much a typical run gains, so it strips out the effect of simply running the ball a lot. Gaining more than five yards a carry means the offense regularly faces second-and-short, which keeps the whole playbook open and takes pressure off a quarterback who is not the regular starter.

That formula carried the Monday night win over Philadelphia. Keenum, making his first start in 1,009 days, threw for 247 yards and two touchdowns and ran in a third, and the offense stayed on schedule all night. Bagent, who cleared concussion protocol last week, has been practicing fully, so Johnson has two options he trusts.

Geno Smith is the challenge

The Jets arrive with a quarterback in excellent form. Geno Smith leads the NFL with a 75.5 percent completion rate, has four touchdowns and no interceptions, and his 110 passer rating is the highest by a Jets quarterback through three weeks in franchise history. Passer rating combines completion rate, yards per attempt, touchdowns and interceptions into one number, and anything above 100 is very good.

One matchup inside the matchup: the Jets note that Smith has been especially effective against single-high coverage, the look where one safety patrols deep and the rest of the defense plays closer to the line. Chicago’s defense uses that look on about 60 percent of opposing dropbacks, one of the higher rates in the league. How Dennis Allen mixes his coverages will be one of the quieter keys to the afternoon.

A defense that has found its footing

After allowing 37 points in the opener at Carolina, the Bears have held back-to-back opponents under 10 points for the first time since 2012. Against the Eagles they allowed 248 yards, held Philadelphia to 2 of 9 on third down and forced three turnovers. Because the season is only three games old, the early points still weigh on the season-long yards-per-play figure, so the recent trend is the better guide. The secondary will be without cornerback Kyler Gordon, who was ruled out, while running back D’Andre Swift practiced fully on Friday and carries no injury designation.

New York’s defense will test Chicago too. The Jets rank second in the league in total defense and expect safety Minkah Fitzpatrick back in the lineup. There is also a familiar connection on the sidelines: Jets head coach Aaron Glenn was Detroit’s defensive coordinator while Johnson ran the Lions’ offense, so both men know each other’s thinking well.

What’s next

Kickoff is noon Sunday at Soldier Field. After that, the Bears head to Green Bay for Week 5. Counted from Sept. 20, Williams’ three-to-four-week recovery window points to a return somewhere between the Packers game and the Week 6 trip to Atlanta, depending on how the hamstring responds.