SANTA CLARA, Calif. - Marcus Martin is the youngest of five children. And he will be the youngest of five 49ers offensive lineman, by far, Sunday when he's slated to make his NFL debut against the St. Louis Rams.
Martin, a 20-year-old rookie, is taking over for the injured incumbent Daniel Kilgore, who suffered a broken lower leg in the team's last game in Denver before the bye week.
By all accounts, Martin is beyond his years - which factored into forgoing his senior season at USC to enter the NFL draft, where he was viewed by many as the best prospect at the position. San Francisco used a third-round pick on Martin in May.
"I started as a freshman at USC, 17 (years-old), and I had to become a mature very fast," Martin said. "It just happened. I’m thankful for all the opportunities that I had."
Martin is coming off an injury of his own, an acute dislocation of his left kneecap in Week 3 of the preseason, which prevented him being active in any game to this point.
Starting as a rookie is difficult enough, but Martin is playing perhaps the most mentally demanding position along the offensive line. He will be responsible for changing protections and blocking assignments in both passing and running plays.
In essence, Martin becomes in charge of four other linemen at least five years his senior.
Martin practiced as the starter for the first time Monday, earning rave reviews from head coach Jim Harbaugh.
"He was impressive today," Harbaugh said of Martin after that practice. "Feel good about what he’s done leading up to now, the position he’s put himself in. As we’ve talked about before, he’s been very good in the classroom and he’s able to carry that onto the field."
During his time on the sideline during games, Martin said he was constantly in the ear of offensive line coach Mike Solari, making calls and reading defensive fronts.
"That was a key component of rehabilitation," said Martin, "because most guys fall off mentally and allow themselves to just focus on the physical aspect. But I think playing good football is being consistent mentally and physically. My time off helped me a lot."
Martin will be thrown into the fire early against one of the league's best young defensive lineman in Rams rookie Aaron Donald. After getting taken by St. Louis with the 13th-overall pick in the spring, Donald has graded out as the league's second-best defensive tackle, according to Pro Football Focus' metrics.
"I’m excited about all of the competition, as always," Harbaugh said. "Look forward to watching Marcus compete."
Donald will line up opposite Martin for the majority of Sunday's game.
"He’s a tremendous player," Martin said of Donald. "Their front seven is great. I just got to be prepared, to battle. It’s going to be a fight for a very long time. You just got to understand what’s being presented."
The 49ers offensive line has been battling cohesion issues all season. The team's projected five starters played just one quarter together all year (the first quarter against Philadelphia Sept. 28). They won't have Kilgore for the remainder of the season, but they will have a chance to develop the chemistry they have struggled to find going forward.
Right tackle Anthony Davis is poised to start consecutive games for the first time all season Sunday while left guard Mike Iupati has been cleared to play after suffering a concussion in Week 6's win over the Rams.
In fact, all players on the 49ers active roster were healthy and present at the start of Wednesday's practice for the first time in 2014.
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