Brock Purdy concussion: A look at Darnold’s backup history and the 49ers’ reserve QB performance under Shanahan

Brock Purdy is in the NFL’s concussion protocol and the 49ers may again have to turn to their backup quarterback, who is Sam Darnold this season.

Darnold arrived in the offseason after Jimmy Garoppolo, the No. 2 last season, left for the Raiders in free agency as the 49ers picked Brock Purdy, last year’s third-stringer, as their new starter.

The quarterback injury carousel is not a device unfamiliar around the league, but the 49ers’ version brings particular intrigue because of its history: Steve Young supplanted Joe Montana; Colin Kaepernick took over for Alex Smith; and Purdy replaced Garoppolo and Trey Lance.

So, what can fans expect if Purdy is unable to start Sunday’s game against the Bengals?

The 49ers have been positive since training camp about Darnold learning coach Kyle Shanahan’s offense, but there isn’t much to parse from this regular season: He is 1-of-1 passing for 1 yard. In the preseason, he was 22-of-33 for 282 yards, two touchdowns and one interception over three games.

He did not play in the first 11 games of last season with the Panthers after suffering a high ankle sprain in training camp and did not get the starting job back until Week 12. He went 4-2 as a starter, though he completed just 58.4% of his passes. He amassed 1,143 yards, seven touchdowns and three interceptions with a QBR of 51.4, right around average.

The prior season, he was Carolina’s starter for the first nine games before suffering a concussion and losing the starting job. He returned to relieve an injured Cam Newton in a Week 15 loss against the Buccaneers, then lost road starts in New Orleans and Tampa Bay to finish the season. Over those three games, he was 61-of-100 for 541 yards, two touchdowns and two interceptions.

Here is how 49ers backups have fared under Kyle Shanahan (record as starter; stats cumulative for full season):

2022

Jimmy Garoppolo: 7-3 record, 67.2% completion, 2,437 yards, 16 touchdowns, 4 interceptions, 56.3 QBR

Brock Purdy: 5-0 record, 67.1%, 1,374 yards, 13 TDs, 4 INTs, 67.5 QBR

Playoffs

Purdy: 2-1 record, 41-63 (65.1%) passing, 569 yards, 3 TDs, 0 INT, 70.8 QBR

Josh Johnson: No starts, 7/13 (53.8%) passing, 73 yards, 0 TD, 0 INT, 14.3 QBR

2021

Trey Lance: 1-1 record, 57.7%, 603 yards, 5 TDs, 2 INTs, 33.4 QBR (38 carries, 168 yards, 1 TD)

2020

Nick Mullens: 2-6 record, 64.7%, 2,437 yards, 12 TDs, 12 INTs, 36.3 QBR

C.J. Beathard: 1-1 record, 63.5%, 787 yards, 6 TDs, 0 INTs, 46.0 QBR

2019

Jimmy Garoppolo made every start, including the playoffs, and was the only QB to throw a pass.

2018

Nick Mullens: 3-5 record, 64.2%, 2,277 yards, 13 TDs, 10 INTs, 51.7 QBR

C.J. Beathard: 0-5 record, 60.4%, 1,252 yards, 8 TDs, 7 INTs, 41.5 QBR

2017

C.J. Beathard: 1-4 record, 54.9%, 1,430 yards, 4 TDs, 6 INTs, 53.4 QBR

Jimmy Garoppolo (acquired via trade and inserted as starter): 5-0 record, 67.4%, 1,560 yards, 7 TDs, 5 INTs, 82.7 QBR