The Dallas Cowboys employed one of the worst defenses in the NFL in 2020, a sieve that couldn't slow a junior varsity operation.
Speaking Thursday, McCarthy said the Cowboys tried to do too much last season, which led to the struggles.
"We tried to change too much on defense, if you're looking for a mistake," he said, via Michael Gehlken of the Dallas Morning News. "And I don't think we made a mistake. We just didn't get it done. We went in with too much volume."
As he did throughout the season, McCarthy defended Nolan, noting "it's not just one guy," as to why the defense struggled.
Under Quinn, the Cowboys believe a simplification of scheme and game-planning will help improve a unit that lacks the depth of talent. McCarthy called Quinn a "huge asset to our football operations."
McCarthy also noted that, with the league anticipating a virtual offseason, the Cowboys must do a better job installing their defense than they did last year during the COVID-19 pandemic.
"We need to do a better job in the virtual component of it," McCarthy said.
While the Cowboys haven't added any big-name defensive players in free agency, expect those additions to come in the 2021 NFL Draft.
"I wouldn't be surprised if we take some defensive players in the draft," McCarthy joked knowingly.
As for veteran players already on Dallas' roster, McCarthy added that he hasn't "personally" moved on from defensive end Aldon Smith, despite reports the Cowboys have informed him they're moving on. McCarthy also announced that Cowboys defensive lineman Tyrone Crawford is retiring after nine seasons in the NFL, all in Dallas. Crawford played 112 games with the Cowboys, starting 79, earning 25 total sacks and 194 tackles.