Cardinals star cornerback Patrick Peterson is among the marquee players set to return on defense in 2018.

If the 2018 NFL season began today, the Cardinals would be running some sort of funky Wildcat formation on offense, and Bruce Arians would not be around to call the plays.

It's clear the Cardinals have some work to do in order to fill critical holes at quarterback and head coach, as well as other spots on offense. But amidst those inevitable changes, the Cardinals should be relatively stable on defense.

Last year, the team lost five defensive starters in free agency. This year, the vast majority of the impact pieces are under contract for 2018, and the starters that aren't – cornerback Tramon Williams, linebacker Karlos Dansby, safety Tyvon Branch and defensive lineman Frostee Rucker – are all older than 30, an age where players don't generally command an exorbitant salary.

The Cardinals' defense started the season slowly, but finished sixth in yards allowed per game (310.9), and was ranked fourth in the NFL by Football Outsiders.

Impact players under contract for next season include outside linebacker Chandler Jones, cornerback Patrick Peterson, outside linebacker Markus Golden, safety Budda Baker, safety Tyrann Mathieu and money linebacker Deone Bucannon.

There are also youngsters with tantalizing potential -- former first-round picks Haason Reddick and Robert Nkemdiche, as well as breakout defensive lineman in Olsen Pierre. Add in stable veterans Antoine Bethea, Corey Peters and Josh Mauro, and it seems clear the Cardinals' defense will once again be a strength next season.

"You add those pieces back, and add maybe some more in the draft, it could be a very dominant defense," Arians said late in the year.

The defense underachieved early in the season before hitting its stride down the stretch. Defensive coordinator James Bettcher believes the plethora of new faces contributed to the slow start. The Cardinals had enough talented players to excel early, but a lack of chemistry meant they could often be a step slow in critical situations.

"There are just snaps on the field where you can't practice this motion or you don't get that adjustment," Bettcher said. "Things happen fast, and just knowing how they are going to play off each other is so critical. Talking about down after down and game after game, I've certainly seen that (improvement) the second half of the season."

As it currently stands, the Cardinals' only glaring hole on defense seems to be at No. 2 cornerback because of the impending free agency of Williams. If he is re-signed or General Manager Steve Keim finds a comparable piece this offseason, the defense will look formidable.

Maybe most importantly, it will be stable. Keim has many crucial choices to make in the coming months, but unlike last offseason, the defense should only feature some tinkering rather than an overhaul.