WEST LAFAYETTE, Ind. — They call themselves the firefighters. Iowa defensive coordinator Phil Parker and his defense earned that nickname last year, when the unit was largely the reason the Hawkeyes finished 8-4 and earned a trip to the Outback Bowl.

Through five games this season, Iowa’s defense has been a crucial reason that the team is 4-1 (1-0 Big Ten). While the offense has struggled to establish an identity, the defense has been stout and consistent.

“We love playing defense,” defensive tackle Carl Davis said following Iowa’s 24-10 victory over Purdue on Sept. 27. “That’s what we came here to do. We go out and play to the best of our ability, and we try to have fun out there. If you have fun out there, you make plays.”

On Sept. 27, it was just another day at the office for Iowa’s defense. The unit allowed 156 total yards — 65 in the first quarter. Purdue moved the chains just nine times all game.

After a nine-play drive that led to a field goal in the second quarter, Purdue’s next 10 drives ended with either a punt or interception — and that’s excluding a one-play drive to end the half.

The only time the Boilermakers found the end zone was when safety Frankie Williams intercepted a C.J. Beathard pass and returned it for a touchdown. The lone time Purdue scored on Iowa’s defense was that second-quarter field goal.

There were also things the defense did that won’t show up on the stat sheet, such as when the Hawks sacked Purdue quarterback Danny Etling on back-to-back plays to push the Boilermakers 18 yards back and out of field-goal range in the first quarter.

“The one constant was our defense played, I thought, pretty well start to finish,” head coach Kirk Ferentz said. “They really did a good job.”

Recently, the number of players seeing action on the defensive side of the ball has been growing; against Purdue, 21 different defensive players participated for Iowa. The players noted a difference in energy because of the rotation.

Since allowing 17 second-half points to Iowa State on Sept. 13, the Iowa defense allowed just 3 combined points in the second halves against Pittsburgh and Purdue. This was around the time the decision to rotate more occurred.

“They’re hard-nosed players,” Louis Trinca-Pasat said about the rotation players. “They know what they’re doing. Coach [Reese] Morgan has everyone focused, they know they’re going to get some reps in there. It helps us stay fresh. They’re doing a good job; they’re going to keep getting better.”

So far this season, Iowa has allowed just 17.2 points and 310.4 yards per game. Those rank 21st and 19th in the nation, respectively. The firefighters, just as they were a year ago, are largely the reason the Hawkeyes have been successful through the season’s first five games.

Just don’t expect them to make that statement.

“The thing is, we never want to think that we’ve got our footing, because that’s when we get complacent, and that’s when we stop improving,” Trinca-Pasat said. “We just have to look at our mistakes and improve on those.

“If we do that, we’ll keep getting better.”

Follow @JacobSheyko on Twitter for updates, news, and analysis of the Iowa football team.