Glenn Dorsey would be excused for using his peripheral vision while playing on Sunday.
After all, the last time Dorsey's 49ers faced the Seahawks – in Week 2 at Seattle – the man he replaced in the lineup was lost for the season.
Cue the gruesome highlight: Ian Williams' ankle breaking on an unannounced cut-block by guard J.R. Sweazy.
How will Dorsey guard against Seattle's perfectly legal yet very perilous run-game tactic?
"That's the magic question," Dorsey said before Thursday's practice. "That's the question of the day.
"It's a part of the game, and it's part of the scheme they do. You just have to be aware and cognizant of the fact that somebody can come and cut-block you. You have to move your feet and be aware at all times."
Dorsey will be helped by his athleticism when the two teams meet at Candlestick Park as part of Week 14 action.
At 297 pounds, he is not the NFL's largest in a position group with players checking in on the scales at 340-plus pounds. This is part of the reason defensive coordinator Vic Fangio and San Francisco targeted Dorsey in free agency last offseason.
"We love his size," said Fangio, who added that Dorsey played his best game to date in Week 13 against the St. Louis Rams. "We don't like big heavy guys. We want some guys that can do the job at the point but still have some movement in them. And he fills that bill."
Still, Williams could move around, too, and look what happened to him.
Seahawks coach Pete Carroll, who ascribes to the philosophy that no penalty is a good penalty, expressed sympathy for the unfortunate play involving Sweazy in September. He said he and his players never want to see an opponent injured.
"It is a legal play to cut at the line of scrimmage in the interior line. There may come a time, with all the safety issues at hand, when the competition committee frowns upon it and takes a turn a different way," Carroll said. "I wouldn't be surprised if that came about."
For now, the way the rules stand, it remains a mystery how exactly a defensive lineman can protect himself in such a situation.
When asked how he coaches his lineman, Fangio provided a direct, Fangio-like response.
"You've just got to get in a good position, stay square to the line, get your hands and feet working for you," he said, pausing briefly, "and know that they do it."