Seneca Wallace wore a number of hats on Sunday in San Francisco.

He also had two helmets.

One is equipped with a radio transmitter given to NFL quarterbacks. That’s the one Wallace would wear should he replace Matt Hasselbeck at quarterback.

Wallace’s other helmet has no radio, just the run-of-the-mill model that every player other than the quarterbacks wear. That’s the one Wallace wore onto the field for his four plays Sunday when he put on his run-catch-pass show in San Francisco.

The Seahawks even had a person on the sideline responsible for holding onto one of the helmets at all times and making sure Wallace had the right one.

“Now tell me we’re not thorough,” Holmgren joked.

Equipment manager Eric Kennedy found someone just for that task of holding one of Wallace’s helmet. One problem. Holmgren didn’t recognize him so when the coach saw an unfamiliar fellow holding a Seahawks helmet on the sidelines, he worried a heist was underway.

“I thought he was stealing one of our helmets,” Holmgren said.

No, the coach was told. That’s just Wallace’s helmet.

A knight has a squire to bring him his weapons, Wallace had an assistant to hold onto one of his helmets.

NFL rules allow the quarterback to have a radio transmitter in his helmet that allows him to hear instructions from the coach until the final 15 seconds of the play clock. The rules also say the offense can only have one radio-equipped helmet on the field at a time. That’s why all the radio-equipped helmets have a green sticker on the back. It allows referees to keep track. Holmgren said a team would receive a pretty substantial fine if it violated that rule.

Holmgren was on the competition committee when the one-helmet restriction was first implemented, and he said it was prompted by examples such as the Steelers’ use of Kordell Stewart. Pittsburgh could move Stewart to wide receiver and bring another quarterback into the game, thereby giving the Steelers the possibility of having two players with radio-equipped helmets on the field. That led to the resolution that even if a team had multiple quarterbacks on the field at the same time, only one of them could have a helmet.

So that explains why Wallace had two helmets to account for all his jobs on Sunday.

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Offensive lineman Ray Willis apparently suffered a knee injury. He was icing the injury and then wearing a brace and had crutches in the locker room.

Running back Alvin Pearman suffered a knee injury and left the locker room on crutches.

Defensive tackle Rocky Bernard suffered an injury to his leg in the first half, but returned without missing a series.

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RB Alvin Pearman was placed on injured reserve, which was expected after he suffered a season-ending knee injury on Sunday in San Francisco. Pearman suffered a torn anterior-cruciate ligament (ACL) in his knee.

DB Kevin Hobbs was moved from the practice squad to the active roster to take Pearman’s place.

LB Cameron Jensen was released from the practice squad, leaving two spots on the eight-man unit. T Kyle Williams and LS Jared Retkofsky were signed to the practice squad. Williams was with the Seahawks in training camp, and his addition is to provide some depth at tackle with Ray Willis expected to miss the next six weeks or so with a sprained knee. Now, Williams won’t be dressing or anything. Floyd Womack and Tom Ashworth are both ahead of him in terms of depth at tackle, but he presumably would provide some insurance.

More eyebrow-raising is the addition of Retkofsky. Coach Mike Holmgren mentioned on Monday that the snap may have played a role in the punt the 49ers partially blocked on Sunday. Derek Rackley is the Seahawks’ current long-snapper, taking over the job after J.P. Darche was injured last season.

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By now Shaun Alexander says he’s used to the idea of having a cracked bone in his left wrist. Especially since the Seahawks star running back says the injury took place in Week 1 against Tampa Bay, and a crack developing was expected. “All these questions would have been tough to answer three weeks ago,” Alexander said on Thursday.

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What will the 49ers do on Sunday? You don’t need to do the math, I will. The 49ers rank No. 29th in passing yardage in the NFL, and the only thing that stopped Frank Gore against Seattle was the final whistle.

Seattle’s run defense figures to be the key to this afternoon’s game. That aspect of the Seahawks defense was a strength in 2005 and really fell apart the second half of last season. Here’s a breakdown of the past two seasons, separated into first and the second half:

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Step One in the NFL’s new anti-steroid program: Separate the boys from the girls. In an attempt to stem the use of steroids among high school athletes, the league launched a $1.2 million education program Tuesday. Working through eight NFL teams, the program is expected to reach 20,000 students in 40 high schools during this school year.

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San Francisco quarterback Alex Smith suffered a right shoulder injury when Rocky Bernard sacked him on third down of the 49ers’ first possession. His return was announced as questionable. Trent Dilfer replaced Smith during the 49ers’ second possession.

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