With the 49ers down 18 points in the second half, injuries to the offensive line started to pile up. Starting left tackle Trent Williams (groin), backup left tackle Jaylon Moore (concussion), and left guard Aaron Banks (toe) exited the game with injuries. Midway through the fourth quarter, Purdy was operating from behind a less-than-ideal line of Colton McKivitz at left tackle, Ben Bartch (practice squad player elevated for this game) at left guard, Jon Feliciano at right guard, and Spencer Burford at right tackle. Woof. Jake Brendel was the only one who remained at his usual center position. Purdy was sacked twice behind that line and briefly exited the game with a stinger, the same stinger he suffered against Arizona the previous week.
49ers backup quarterback Sam Darnold entered the game for Purdy. He took over at the Baltimore 31 and went on to score on a 12-yard touchdown pass to rookie Ronnie Bell, cutting the lead to 14 with a little over six minutes left in the fourth quarter. Purdy was shortly thereafter cleared to return to the game but Kyle Shanahan appeared to tell Purdy on the sideline that his night was done. Darnold played the rest of the fourth quarter and finished 8 of 14 for 81 yards, a touchdown, and an interception of his own.
When asked if Purdy could have come back in, Shanahan admitted "probably" but acknowledged the stinger and having three offensive linemen out played into the decision to keep him out.
It would be silly to think that Purdy's poor play didn't have at least a little to do with Shanahan's ultimate decision. But given that, the score, the makeshift offensive line, and wanting to preserve the overall health of your starting quarterback, it was a sound choice at that point in the game. Of course, the internet narratives will have you believing otherwise. The expectation is that Brock Purdy will start next week against the Washington Commanders.