Chargers quarterback Taylor Heinicke hands the ball off to running back Gus Edwards during the fourth quarter on Sunday.

(Matt Freed/Associated Press)

That’s why Taylor Heinicke is here.

The Chargers traded a conditional sixth-round pick to the Atlanta Falcons for the 10-year veteran, knowing they needed to upgrade their backup quarterback in case Herbert got injured. The moment no one was waiting for came Sunday.

With only 24 days of experience in the organization, Heinicke entered the game in the third quarter and completed both of his pass attempts for 24 yards, but was sacked three times behind an offensive line that lost left tackle Rashawn Slater to a pectoral injury.

“I wish we would have given him a little more time for the surgery, but I was pleased with his performance,” head coach Jim Harbaugh said of Heinicke. “He’s a competitor. Competitors are welcome here at the Los Angeles Chargers.”

Acting reserve Easton Stick had a head start, having played in all three preseason games, but Heinicke caught up by spending three weeks immersed in the playbook. The system was so complicated that at first he even had trouble saying a play out loud.

He was inactive for the first two games to get his game in order. Then, late last week, when Herbert was limited in practice, Heinicke took over the majority of the training sessions, which helped him comfortably lead the offense despite the injury midway through the game.

Although Harbaugh immediately dismisses any “what ifs,” Heinicke has had to live in hypotheticals for a decade. The longtime backup has made it his mission to plan for just in case, and is ready to do so again while Herbert oversees the high ankle sprain.

“We will see how this week goes,” said Heinicke.