Los Angeles head coach Jim Harbaugh dug deep into the football rulebook to bring the Chargers within one score of the Denver Broncos just before halftime with a fair catch kick.

The Chargers forced a Broncos punt after Justin Herbert's second interception in as many games. On the punt, Broncos cornerback Tremon Smith committed fair catch interference on Chargers returner Derius Davis. That set Los Angeles up with the ball at the Broncos' 47-yard line, with one untimed down remaining in the half.

Harbaugh opted to attempt a fair catch kick -- a rarely used rule that allows a team to attempt a field goal from the spot on the play immediately following a fair catch. Cameron Dicker drilled the 57-yarder. The Chargers sideline erupted.

But what exactly is a fair-catch kick? Here's what you need to know:

The NFL's official rulebook defines it as either "a drop kick or place kick without a tee from the spot of a fair catch in an attempt to score a field goal."

Teams can attempt a fair catch kick if time expires during a play where a player makes a fair catch. The receiving team is granted an untimed down but only to attempt the kick.

The Chargers however could've chosen to run a play from scrimmage as the Davis' fair-catch was interfered with.

The last successful fair-catch kick was in 1976 coincidently by a Chargers kicker. Ray Wersching hit a 45-yarder against the Buffalo Bills at the end of the first half.

Sean Payton often spends time during OTAs and training camp practicing rare and even obscure scenarios.

"It might only come up once every few years," he'd say of a given situation, but he has always been intentional about covering as many end-of-half and end-of-game scenarios. That included free-kick situations like the one the Broncos encountered at the end of the first half.

"It's a fair-catch, free-kick situation; we practice it," Payton told Amazon sideline reporter Kaylee Hartung at halftime.

The Broncos would not have been in that situation at all with better execution on their final possession. Denver got the ball back with 41 seconds left following an interception by rookie Kris Abrams-Draine, and the Chargers appeared content to let the first-half clock ran out. But the Broncos threw incomplete on second down and Jim Harbaugh called a timeout after a short third-down run with 8 seconds left, setting up the wild final sequence. -- Nick Kosmider, Broncos beat writer