Injuries are piling up on Iowa's defense. How will it affect Saturday's game vs. Michigan?

Through four games there's little surprise about the brightest spot on Iowa's football team. It’s defense.

The Hawkeye unit is among the nation's best in almost every category, including No.1 in scoring defense (5.8 points per game) and No. 6 in total defense (236.2 yards per game). The Hawkeyes also have recorded four defensive scores: two touchdowns and two safeties. 

It's a testament to defensive coordinator Phil Parker and the talented frontline starters, but it's also because of tremendous depth they've built at several positions. The Hawkeyes have built that depth under the mantra "Prepare as if you're the starter.”

It was on full display in Iowa's 27-10 win over Rutgers last weekend. Starting cornerback Terry Roberts was a last-second scratch to injury. Junior safety Sebastian Castro made his first career start and forced a fumble that led to the defense's second score of the game.

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"One guy's down, next man just steps in," defensive back Cooper DeJean said after the team's win. "Everybody's getting reps in practice just preparing to be the starter. We're all watching film together and things like that. So we're all talking, seeing things on film and contacting each other. So I think really just starts with preparation with all of us." 

Beyond Rutgers, defensive depth will play a large role in Iowa's next game against No. 4 Michigan and will persist through the rest of the season. On Tuesday, head coach Kirk Ferentz provided several injury updates, and the Hawkeye defense will be short-handed moving forward.

The biggest news was that junior linebacker Jestin Jacobs will miss the rest of the season due to an injury suffered at Rutgers. It's a tough setback for Jacobs, who returned to the lineup after missing the last 2 1/2 games to a soft-tissue injury in his lower body. Additionally, Ferentz said that Roberts is questionable on Saturday and backup cornerback Brenden Deasfernandes remains out as well. 

Roberts has been a limited participant in practice this week so there is a chance that he can play. Couple that with existing injuries such as defensive lineman Yahya Black, and Iowa could be without several important pieces on defense this weekend. But in some ways it's something they've gotten used to this year. 

One of the biggest storylines from Iowa's spring practice was the number of injuries to starters. The silver lining was that it allowed for backups to receive starter reps, and several months later those practice reps are paying off. 

"I think that was a great time for us guys that just didn't have a ton of game experience," reserve linebacker Logan Klemp said. "I think that was like a big time for us to kind of develop and just getting reps with the (first team) and operate in that way." 

Klemp was thrust into playing time in Iowa's opener against South Dakota State when Jacobs left with his first injury. Now Klemp is a rotation player along with fellow reserve linebackers Jay Higgins and Kyler Fisher, who earned rotational snaps by way of impressing the coaches during spring practice. Now they'll be counted on through the rest of the season with Jacobs out. 

"Those guys did a really good job in the spring," Ferentz said after the Rutgers game. "They gained a lot of confidence from the coaching staff by what they did. You need depth because you're always going to contend with injuries and that's certainly the case for us right now." 

The secondary, particularly cornerback, is where the Hawkeyes have been hit hardest. Roberts and Deasfernandes' injuries followed starter Jermari Harris', who is also out for the season. This comes at a time when Iowa will face its most dangerous vertical pass threat yet in Michigan. Sophomore quarterback J.J. McCarthy leads the nation in yards per attempt with a whopping 11.6-yard metric, and his top three wide receivers (Ronnie Bell, Roman Wilson and Cornelius Johnson) are all averaging at least 15 yards per catch. 

Getting pressure on the quarterback will help alleviate concerns on the back end. Redshirt sophomore Lukas Van Ness is primarily playing defensive tackle, despite plans to play defensive end this year, to mitigate the loss of Black. He led the team with nine quarterback pressures against Rutgers. True freshman Aaron Graves is another name to watch, he's played in Iowa's last two games recording six tackles and 2.5 sacks. 

Iowa still has Riley Moss and Cooper DeJean as starters at corner but behind them is uncertainty. Redshirt freshman Jamison Heinz and true freshman TJ Hall are the listed backups behind them. Senior safety Kaevon Merriweather noted that freshman defensive backs playing in big games isn't new, citing Moss and former player Julius Brents starting against Minnesota in 2018. He added that their maturity is why they're being trusted to potentially play this weekend. 

"(TJ and Jamison) come in and work as if they're older guys," Merriweather said. "They come prepared and they make sure they're paying attention to the game plan. They're very detailed with everything that's going on. It's just the maturity level to kind of grow up a little bit quicker." 

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Iowa defenders attributed success despite players missing time to the high standard that's placed by Parker and carried out by the players day-to-day. They're not lowering them because of players missing nor will they make excuses. For the players stepping in, it's a chance to make an impression with the opportunity presented. 

"It's interesting, it's not exactly how you want it to come about with injuries and stuff like that," Klemp said. "But it's just being ready for that opportunity. When it comes and being able to step up and kind of show that investment that was made and you're here to make plays, make the adjustments and everything like that."

Kennington Lloyd Smith III covers Iowa Hawkeyes football and men's basketball for the Des Moines Register. You can connect with Kennington on Twitter @SkinnyKenny_ or email him at ksmith@gannett.com.