FRISCO, Texas -- Defensive coordinator Mike Nolan and defensive line coach Jim Tomsula will not be returning to the Dallas Cowboys for the 2021 season, the team announced Friday.

Last season, the Cowboys (6-10) allowed the most points in franchise history (473) and finished 31st in the league in run defense. In the season-ending loss to the New York Giants, they allowed 23 points, including 20 in the first half, to an offense that had not scored more than 19 in five weeks.

The unit played better down the stretch with 12 takeaways in the final four games after getting just 11 in the first 12 games, but that was aided in part by facing backup quarterbacks in Cincinnati, San Francisco and Philadelphia.

"I am appreciative of my relationships with both Mike and Jim, and I am grateful for the contributions that both of them made to our team under difficult circumstances in 2020," coach Mike McCarthy said in a statement. "These are never easy decisions to make, and we wish them, and their families, the very best in the future."

Speaking on 105.3 The Fan in Dallas at different times during the season, owner and general manager Jerry Jones and executive vice president Stephen Jones lamented the jarring scheme switch -- from a 4-3 look to a hybrid look -- made by the Cowboys during an offseason in which the coaches could only meet virtually with the players.

Unable to get hands-on experience until the start of an abbreviated training camp, the Cowboys defense struggled badly. They finished 23rd in yards per game (31st vs. the run, 11th vs. the pass) and 28th in points (29.6). The Cowboys allowed 69 plays of 20 yards or more, including 51 passes and 18 runs.

In the three other times the Cowboys allowed a franchise record in points, the organization either made a scheme change or a coaching change.

After allowing 436 points in 2010, Jason Garrett was named the full-time head coach after taking over for Wade Phillips at midseason, and he hired Rob Ryan as defensive coordinator. In 2013, they allowed 432 points in Monte Kiffin's first year as coordinator, and he was replaced by Rod Marinelli. After giving up 405 points in 2004, Bill Parcells switched from a 4-3 to a 3-4 scheme but kept Mike Zimmer as his coordinator.

Head coach Mike McCarthy and Nolan have a long background together. In 2005, Nolan hired McCarthy as his offensive coordinator with the San Francisco 49ers, which helped propel him to earning the Green Bay Packers head job a year later.

But the defense could not find its footing. While they suffered some injuries to Leighton Vander Esch (collarbone, ankle), Trysten Hill (knee) and Trevon Diggs (foot), they were not hit as hard as the Cowboys' offense.

Their bigger free-agent pickups were either hurt in training camp (defensive lineman Gerald McCoy), did not make the team out of camp (safety Ha Ha Clinton-Dix), were traded (Everson Griffen) or were released because of poor play in the middle of the season (defensive tackle Dontari Poe, cornerback Daryl Worley).

If the Cowboys look in-house for a replacement, George Edwards spent the year as a senior defensive assistant. He was Zimmer's defensive coordinator from 2014 to 2019.

But the first question that must be answered is what type of scheme the Cowboys want to use. In Green Bay, McCarthy employed a 3-4 scheme for most of his tenure. If he wants to continue with the hybrid look Nolan attempted to use, adding players to fit the scheme will be an offseason priority. In all but three years of his time in Green Bay, the Packers used a 3-4 scheme.