SANTA CLARA, Calif. — After another loss to the Kansas City Chiefs, Nick Bosa wasn’t excited to go back and watch the tape. There was, however, one thing he wanted to see: after the loss, his father, John, alerted him to how well rookie safety Malik Mustapha played.

As a defensive end, Bosa doesn’t have the opportunity to see such things in real time, but when he did turn on the film, he co-signed his father’s take.

“He was like, Mustapha was flying around and then I watched the tape and saw that,” Bosa said. “He looked great.”

These days, it’s not difficult to turn on a 49ers game and see a rookie succeeding in a prominent role. The team entered this season as the league’s third oldest (with an average age of 26.9) and, in the past, has had little need for rookie contributions because of the many veterans on the roster. But because of an extensive injury list, the rookie class is quickly proving its value this season.

Last season, 49ers rookies played 1,760 total snaps in 17 games, with safety Ji’Ayir Brown leading the way in playing time (554 snaps).

Through eight games in 2024, San Francisco’s nine rookies have combined to play 1,665 snaps, which ranks seventh in the NFL. Guard Dominick Puni has played the most (549 snaps) among all rookies in the league in that span. And he’s been good: Puni ranks 14th among guards in pass block win rate (94.1%).

While injuries have hit the 49ers hard at safety, on both lines, in the secondary and at running back and wide receiver, this youth movement wouldn’t be happening if San Francisco didn’t feel so good about the group as a whole.

“Honestly, I think this has been one of the most ready groups of rookies that we’ve had,” linebacker Fred Warner said. “It’s interesting because we haven’t had rookies that have needed to be ready to go, but now since they have their numbers called and they are ready, it has been really good.”

Although none of the team’s rookies were expected to start or even necessarily push for a starting job, 49ers coach Kyle Shanahan was immediately impressed with the maturity and competitiveness of the group as far back as May.

In the opening days of training camp, the first wave of injuries struck San Francisco at guard. Spencer Burford broke his right hand and Jon Feliciano dealt with a nagging knee injury. Enter Puni, the third-round pick out of Kansas who had played all over the line and started 38 games in college.

That experience showed up quickly to Shanahan and offensive line coach Chris Foerster, both of whom noted that Puni looked right at home nearly from the moment he stepped in with the No. 1 offense. Puni was so effective that even when Burford returned, there wasn’t really a decision to be made: the job was his.

“That’s a perfect example for everybody,” Shanahan said. “You try to tell stories like that all the time to these guys. Don’t ever think it’s a redshirt year. There’s no such thing in this league. And it’s not just rookies, it’s the same for practice squad guys. You’re only, usually it’s one injury away, but sometimes it’s two, but it’s a matter of time. Some guys can get lucky and people stay healthy the whole time and they can really develop the right way. But usually in this league you rarely get that.”

While Puni was the only rookie to start Week 1, Mustapha, a fourth-round pick out of Wake Forest, joined him in Week 4 after playing 83 snaps in the first three weeks.

Like Puni, Mustapha has played well — 29 tackles, an interception and two pass breakups. According to NFL Next Gen Stats, Mustapha has been targeted 10 times in 138 coverage snaps. He’s allowed a 20% completion percentage (the best mark for any NFL player with at least 50 snaps) for 27 yards and one touchdown.

He could hold down the job for the rest of the season depending on if and when Talanoa Hufanga is able to return from torn ligaments in his right wrist. Others, such as second-round cornerback Renardo Green, who appears to have overtaken Isaac Yiadom as the third corner, fourth-round running back Isaac Guerendo and seventh-round linebacker Tatum Bethune have all played more than 100 snaps.

And that doesn’t even account for the two drafted receivers — first-round pick Ricky Pearsall and fourth-round selection Jacob Cowing — who now have had expanded roles after injuries to Brandon Aiyuk (torn right ACL and MCL), Jauan Jennings (hip) and Deebo Samuel Sr. (pneumonia symptoms, ribs and oblique).

After recovering from a gunshot wound suffered during an armed robbery attempt in late August, Pearsall was activated from the non-football injury list before the Oct. 20 game against Kansas City. He made his first NFL start in Week 8 against the Dallas Cowboys and will play a pivotal role the rest of the way even as Samuel and Jennings return.

Aiyuk’s injury and Samuel’s illness forced Pearsall into playing more than expected and finished with 77 yards from scrimmage vs. the Cowboys. In the week before that game, Mustapha approached Pearsall and told him it was his time to make his mark.

“(He) said it perfectly, just being the cherry on top of everything,” Pearsall said. “I think ever since we got drafted and seeing the guys that we picked up, I knew we had a strong class … I got to see everybody perform from the sideline unfortunately, but still got to see all the talent that this rookie class has. I’m excited to add to it.”

At 4-4, the 49ers are expecting some of their most important injured players such as running back Christian McCaffrey — who began practicing this week ahead of Sunday’s game at the Buccaneers (1 p.m. ET, Fox) –, linebacker Dre Greenlaw, kicker Jake Moody and, potentially, Hufanga, to return in the season’s final two months.

That could slice into the playing time for some of the rookies but, as they’ve already learned, their number will be called again. It’s why left tackle Trent Williams, who is in his 14th year in the NFL, calls it the “most productive” rookie class he’s been around in his career.

And, as Williams points out, this rookie class will eventually turn into the next generation of players the 49ers are counting on to keep them competitive well into the future. That all is still to be determined even though the early returns are promising.

“It’s always important to hit on your draft picks,” Williams said. “That’s the only way you kind of keep the locker room improving, trimming the fat. … Even though we do have a lot of high-earning players, the draft picks are really the lifeblood of the team year in and year out, so it’s extremely important.”