The hit flipped him clear over, from an attempted slide on his rear end to a face-down sprawl on the grass near the sideline. It rattled his helmet, bloodied his chin, clouded his mind. When the Washington Redskins’ medical staff sat him down and asked him standard concussion-test questions, Robert Griffin III couldn’t tell them what the score was or what quarter it was.

The hit, a shoulder-to-helmet sledgehammer delivered by Atlanta Falcons linebacker Sean Weatherspoon in the third quarter of the Redskins’ 24-17 loss, left Griffin with a “mild” concussion, according to Coach Mike Shanahan — although many in the medical community reject the notion of any concussion being “mild.”

Griffin would not return to the game. He was helped to the sideline, where his chin was stitched up, then taken to a darkened observation room behind the Redskins’ sideline. Once it was determined he had concussion symptoms, Griffin was led to the Redskins’ locker room — walking off the field slowly, but still reaching up to high-five the hands of fans reaching over the railing towards him — and eventually sent home.

“He’s good,” Griffin’s father, Robert Griffin Jr., said in a text-message response to a question late Sunday afternoon regarding his son’s condition. The quarterback’s father, who was at FedEx Field on Sunday, added: “Not happy watching game ending.”

A few hours later, Griffin himself sent out word to his Twitter followers: “Thank you for all the prayers & support I’m ok and I think after all the testing I will play next week.”

According to a team spokesman, Griffin was sent home to rest and will not undergo any further tests until Monday. Per NFL rules, he would need to be declared free of concussion symptoms by an independent neurologist before resuming practice or speaking to the media.

Griffin had been living close to the edge all season, at times being too slow to slide to avoid a hit, at other times absorbing big hits on quarterback-option fakes. But he had always gotten up and kept playing, until Sunday. By design, the Redskins had scaled back Griffin’s exposure to hits in the past two weeks, and Sunday’s fateful scramble was just his second rush.

Flushed out of the pocket on a third-and-goal pass play from the Falcons 3-yard line, Griffin momentarily saw a path to the end zone, but it closed fast, and Griffin never even got close to the pylon. Realizing he was going to be penned in by the Falcons near the 5, he started to slide — but too late. Weatherspoon, at a full sprint, caught him with his shoulder, flush on the helmet.

Weatherspoon called the hit a “bang-bang” play — though most observers could recall only one “bang.”

“I felt like it was a good hit. I felt like it was a clean hit,” the Falcons linebacker said. “He kind of turned upfield, and I lowered my shoulder on him, and he was [treated as] a runner.”

After the hit, Griffin appeared to make a brief attempt at getting to his feet, but sunk back to the prone position for several more seconds. Eventually, he was helped up, and he walked off the field under his own power, dabbing at his bloodied chin with a towel.

“He said he was cool,” said wide receiver Santana Moss, who checked on Griffin as the quarterback was being treated on the Redskins’ bench. “He gave me the heads-up that he was okay.”

But Griffin wasn’t okay. The cut on his chin was easy enough to stitch up, but once Griffin couldn’t answer basic questions about his surroundings, the Redskins knew that No. 10 was done for the day and that it would be a nervous week at Redskins Park as the team awaits word on his condition.

Mark Maske and Kent Babb contributed to this report.