That's when quarterback Russell Wilson scrambled to his right and tried to stiff-arm linebacker Eli Harold near the sideline. Harold brought Wilson to the ground. The quarterback's left leg bent awkwardly, and he was slow to get up.
"I didn’t know what happened, honestly," Wilson said.
"I was a little worried when it first happened initially. I was getting pulled down. I was like, ‘Uh-oh.’ "
Pete Carroll said after the game that Wilson suffered a knee sprain but "most likely" will be fine for next week's game against the New York Jets. Wilson confirmed that he will have an MRI to determine the extent of the injury but said he'll "be good to go."
After the initial injury, Wilson exited the game for one snap before returning. He handed the ball off twice and attempted one pass before the Seahawks settled for a field goal. On the sideline after the possession, Wilson was tended to by the training staff and fitted for a brace on his left knee.
He underwent a series of tests and put his helmet back on, but Carroll opted to go with backup quarterback Trevone Boykin the rest of the way.
Wilson was having a monster game, completing 15 of 23 passes for 243 yards and a touchdown as the Seahawks' offense exploded in a 37-18 victory.
Entering the day, the offense had managed just one touchdown on 22 possessions. But the Seahawks had everything working against the 49ers. Christine Michael carried 20 times for 106 yards and a pair of touchdowns. Wide receiver Doug Baldwin and tight end Jimmy Graham carried the passing game.
Baldwin had eight catches for 164 yards and a touchdown on 10 targets. Graham had six catches for 100 yards and a score on nine targets. It was the tight end's second-highest yardage total since joining the Seahawks before the 2015 season.
But all eyes now will be on Wilson's injury. He entered the game nursing a high ankle sprain suffered in Week 1 against the Miami Dolphins. That injury slowed him in a Week 2 loss to the Los Angeles Rams. But Wilson looked much better in two-plus quarters against the 49ers and said afterwards the ankle felt great.
Carroll said the offense is hoping to build on Sunday's performance, but that can only happen if the Seahawks have a healthy Wilson. They go into next week's matchup against the New York Jets with a 2-1 record before a bye in Week 5.
This is the first time in Wilson's career that he has missed snaps due to an injury. He stood on the sideline with his left knee wrapped in ice after Boykin took over.
Wilson takes pride in his durability, but it has been a rough start to the season for him physically.