SOUTH BEND, Ind. (AP) — Notre Dame fans might need a flip card to keep track of who is playing on defense when the Fighting Irish face Southern California on Saturday.

Heck, the coaches might need to keep a list available to know who is still available.

Isaac Rochell will be the only Notre Dame defensive lineman to start against USC who was projected as a starter before the Irish opened training camp in August. The only others left from 11 expected starters are linebacker Jaylon Smith, cornerback Cody Riggs and safety Austin Collinsworth — and Riggs and Collinsworth have injuries that could limit their playing time.

Notre Dame (7-4) heads into its rivalry game against USC (7-4) with a defense being held together with spit and baling wire. Coach Brian Kelly described the injuries the Irish sustained as “devastating.”

“That’s why it’s so important to have great depth and continue to build your depth,” Kelly said.

Kelly announced Tuesday the Irish will be without two starting defensive linemen. Nose guard Jarron Jones, tied for sixth with 40 tackles, tore a ligament in his foot against Louisville and is out for the season. Defensive tackle Sheldon Day, with 38 tackles, is out a second week with a sprained knee.

Freshman safety Drue Tranquill, who started two of the past three games and has 33 tackles, is out for the season with a torn anterior cruciate ligament.

The Irish previously have lost starting middle linebacker Joe Schmidt to a season-ending ankle injury against Navy and his replacement, Nyles Morgan, has to sit out the first half against USC because he was called for targeting.

Others missing from the lineup include cornerback KeiVarae Russell and defensive lineman Ishaq Williams, both expected to be starters, and reserve linebacker Kendall Moore, who weren’t allowed to play following an investigation into whether homework and papers they turned in had been completed by others. Reserve defensive lineman Tony Springmann ended his playing career before the season began because of a back injury and linebacker Jarrett Grace still hasn’t recovered from a broken leg last year.

The players left have struggled. The Irish defense has given up 30 or more points for six straight games, the longest such streak in school history, and is giving up an average of 40 points a game during that span.

“If we could have held together some of the key players on a young group, I think it would have definitely served us better. So we’ve got some players that are ascending at the end of the year,” Kelly said. “We would have liked the unit as a whole be ascending, but it’s been difficult with the loss of several key players.”

One of the biggest problems has been giving up big running plays. Through the first seven games, the Irish gave up a total of six runs of 15 yards or more, including none against Stanford or Florida State. Since then, the Irish have given up 14 such runs, including five against Navy and four each against Northwestern and Louisville.

Kelly said part of the reason is communication problems caused by the loss of Schmidt, who was in charge of calling plays and helping get the Irish lined up, and missed reads and coverages. Kelly talked about how Smith was pleased he had been assertive against Louisville and shifted the defense. Unfortunately for the Irish, though, he moved the defense in the wrong direction, leading to a touchdown.

“He thinks he’s making the right decision and he’s growing. He’s ascending as a player. The knowledge base, we’re trying to catch up there,” Kelly said.

With 24 career starts, Smith has the most starts for the Irish of anyone on the defense. And sophomore defensive lineman Jacob Matuska will be making his first career start and linebacker Greer Martini his second against USC as the Irish seek to avoid a four-game losing streak after a 6-0 start.

Notes: Kelly said he doesn’t believe the Irish have to worry about vacating victories because of the academic misconduct investigation, saying athletic director Jack Swarbrick told him “that wasn’t on the table for us right now.” … Kelly said receiver DaVaris Daniels, who wasn’t allowed to play this season because of the academic investigation, is talking with school officials about whether he will be eligible to return. Kelly called it a “complex situation.”