Despite missing copious practice time this week and getting a “questionable” designation to play because of a high-ankle sprain, Los Angeles Chargers quarterback Justin Herbert started Sunday’s game at the Pittsburgh Steelers.

But he did not finish it.

After working out on the field about two hours before the game, Herbert played 2 1/2 quarters before suffering an apparent aggravation of the injury while absorbing a sack from Elandon Roberts during the third quarter.

Herbert stayed in the game but left after the next snap.

“My plan was (at) the first sign of any kind of any limp, he was coming out of the game,” Chargers coach Jim Harbaugh said.

Perhaps in preparation for such a scenario, the Chargers had three quarterbacks active — a rarity in today’s NFL, particularly with the reintroduction of the No. 3 “emergency” QB rule the past two years. While backups Easton Stick and Taylor Heinicke both were on the gameday roster, it was the veteran Heinicke to whom Harbaugh turned after Herbert left the game.

Heinicke, 31, started four games for Arthur Smith’s Atlanta Falcons last season. After getting fired as head coach of Atlanta, Smith was hired as Steelers offensive coordinator.

In one snap plus two full possessions in the game, Heinicke went 2 for 2 passing for 24 yards but was sacked three times and the Chargers netted just 4 yards in his two drives.

The score was 10-10 when Herbert was injured; it ended up a 20-10 Steelers victory.

Chris Adamski is a TribLive reporter who has covered primarily the Pittsburgh Steelers since 2014 following two seasons on the Penn State football beat. A Western Pennsylvania native, he joined the Trib in 2012 after spending a decade covering Pittsburgh sports for other outlets. He can be reached at cadamski@triblive.com.