SANTA CLARA -- When the 49ers season began, three members of the starting defense were 30 years are older. Now we're down to one. Safety Antoine Bethea's, 31, torn pectoral injury and Glenn Dorsey's, 30, torn ACL landed both on injured reserve, leaving only Ahmad Brooks, 31, in the 30-something club.
The injuries follow on the heels of the ouster of Ray McDonald, 31, and the retirements of Patrick Willis, 30, and Justin Smith, 36. Which underscores what NaVorro Bowman, 27, has been saying all season: The 49ers have a young defense. After Brooks, the oldest member is Michael Wilhoite, 28.
At 3-7, the 49ers are looking more toward 2016 as we move down the homestretch of the season and a number of seldom-seen players will get a chance to make a case for bigger roles next year. They are:
DL Arik Armstead, 22. The team's first-round draft pick played a season-high 46 snaps after Dorsey went down on the opening defensive series. Armstead finished with more tackles -- six -- than any other 49ers defensive lineman. To this point, he's been used mainly as a pass-rush specialist and his forte has been breaking down the opponent's pocket. Armstead was credited with a quarterback hit Sunday and Pro Football Focus gave him a plus-2.6 pass-rush grade for the game. Not only will Armstead get more snaps over the last six games, he'll be asked to stop the run, which was Dorsey's strength but not necessarily Armstead's. He'll need to be able to hold his ground -- not easy when you stand 6-7 and have long legs -- and to make plays instead of merely being disruptive. The timing of Dorsey’s injury means that he likely will not be available at the beginning of the 2016 season, either. He is signed through 2016.
DE Tank Carradine, 26. The 49ers want Carradine below the 275-pound weight at which he entered the league in 2013. (He was about 280 on Sunday). The former second-round pick bulked up to 300 pounds as the 49ers turned him into a defensive lineman in their 3-4 system. The plan now is to make him a pass-rush specialist off the edge, which is similar to how he was used at Florida State. Carradine played no snaps against the Falcons and was not even in uniform against the Seahawks. However, the plan is to unveil the reshaped defender at some point before the season draws to a close.
CB Marcus Cromartie, 24. He didn't start Sunday's game. Rather he replaced Kenneth Acker when the latter struggled at the position and Cromartie ended up playing 47 snaps. The 49ers like his size and aggression, and Cromartie is unafraid to get involved on run defense. Cromartie has a hunger about him that the 49ers like. It will be interesting to see if his role expands Sunday against the Cardinals.
QB Blaine Gabbert, 26. No one can base decisions about the most important position on the team one just two games, but Gabbert’s start has been better than expected. He simply looks comfortable running the 49ers’ offense, including his ability to escape pressure and buy extra time. The Seahawks dropped two would-be interceptions, which, coupled with two interceptions against Atlanta (one was Gabbert’s fault) is a concern. The next game against the Arizona Cardinals, whose defense destroyed the 49ers like no other this season, provides another excellent test.
C Daniel Kilgore, 27. By all reports, Kilgore looked good in his first week of practice since breaking his left ankle in October of 2014. Kilgore said he was targeting Sunday's game against the Cardinals for his comeback, and that plan still seems to be in place. Dorsey's ACL injury will open a roster spot that could be filled by taking Kilgore off the physically unable-to-perform list.
S Jaquiski Tartt, 23. The 49ers' second-round pick is auditioning for a starting role in next year's defense. He got mild applause in his first game against the Rams, an ovation in the next one against the Falcons and crickets chirping for Sunday's outing against the Seahawks. Of course, no one on defense plays well when an undrafted rookie running back rushes for 209 yards and the opposing quarterback completes 24 of 29 passes. Russell Wilson picked on Tartt to the tune of six passes for 54 yards, which earned the rookie safety a minus-3 grade from Pro Football Focus.
G Andrew Tiller, 26. Not only did Tiller make his first start Sunday, he played well enough that Jordan Devey remained on the bench throughout the game. From Week 5 through 10, the two had altered series at right guard. The rap on Tiller before this season was that he was good at power blocking but didn't have the movement skills needed in pass protection and in zone run blocking. He's proven otherwise. He, center Marcus Martin and Alex Boone were the only 49ers with positive grades against the Seahawks, according to Pro Football Focus.
RB Carlos Hyde, 24. He was always in next year's blueprint. A league source said the plan was for Hyde, who is dealing with a stress fracture in his left foot, to return to action Sunday against Arizona or perhaps the following week in Chicago. Of course, an earlier plan was for him to play in the game immediately following the bye week. The situation obviously is fluid and dependent on how Hyde feels. When he comes back, look for him to share carries with Shaun Draughn.