A new clarification from the NFL's officiating board may fundamentally alter how teams use the read-option play.

In a video distributed by the NFL's communications staff, vice president of officiating Dean Blandino explains how the league treats quarterbacks who use the read-option.

UPDATE: Friday, Sept. 6, at 8:38 p.m. ET

Here's a video showing San Francisco 49ers head coach Jim Harbaugh's reaction to the news:

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UPDATE: Friday, Sept. 6, at 6:05 p.m. ET

From USA Today's Tom Pelissero:

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The ruling means those quarterbacks are not subject to the protection most around the league have become accustomed to. In recent years, the NFL has attempted to protect defenseless quarterbacks by enforcing stiffer penalties on defenders who hit quarterbacks in the head or dive at their legs. Penalties usually result in 15 yards for unnecessary roughness and a possible fine from the league, depending on the severity.

Blandino says read-option quarterbacks give up their rights because of the uncertainty over who has the ball.

“The quarterback and the running back, they’re both treated as runners. We don’t know who has the football, we don’t know who’s going to take it, so both players are treated as runners,” Blandino said, via Pro Football Talk's Michael David Smith.

Because the nature of a read-option play is to confuse defenses, quarterbacks are not considered "defenseless" again until they're clearly not involved in the play.

“He is still treated as a runner until he is clearly out of the play,” Blandino said. “The quarterback makes the pitch, he’s still a runner—he can be hit like a runner until he’s clearly out of the play.”

A staple of the college game for years, the read-option spread like wildfire during the 2012 NFL season. Quarterbacks like Robert Griffin III, Colin Kaepernick and Russell Wilson (among others) burst onto the scene last year, with their respective teams taking advantage of their unique skill sets and utilizing the read-option heavily to keep defenses on their toes. Each of those three quarterbacks led his team to the playoffs, with Kaepernick's San Francisco 49ers representing the NFC in the Super Bowl.

The proliferation of that offense has led to hand-wringing across the league as defensive coordinators try to figure out how it can be stopped. Green Bay Packers head coach Mike McCarthy, whose defense Kaepernick torched for 181 rushing yards in the playoffs, was one of many coaches to send his defensive staff to colleges to learn more about defending the option.

Leading up to their Week 1 rematch against San Francisco, McCarthy's players have come out in recent days saying they plan on hitting Kaepernick early and often. Linebacker Clay Matthews acknowledged, however, that it will be interesting to see how players toe the line once they realize what refs actually allow on game day.

"We'll see the hits that are legal and what's not legal, but we think our game plan fits within the scheme of the officials and what we want to do," Matthews said, per Matt Maiocco of CSN Bay Area.

49ers coach Jim Harbaugh had also expressed concerns about the brazenness of Green Bay's defensive players. But with the NFL providing clarification Thursday, it's clear that read-option quarterbacks will be seeing far more aggressive shots than they were a season ago.

Nevertheless, finding a middle ground could be the key to the read-option's long-term viability in the league.