It failed miserably, and was a major turning point in the game. The 49ers had a chance to seize momentum early in the first quarter of their eventual 37-27 loss to the Seattle Seahawks on Sunday, but they blew it in spectacular fashion.
After a tremendous defensive possession to open the game, San Francisco's offense took over and crossed midfield. Facing a crucial third-and-5 at Seattle's 37-yard line, the 49ers went in motion before the snap, morphing from an alignment in which quarterback Jimmy Garoppolo was under center to one in which running back Jerick McKinnon would take the snap in a Wildcat formation.
McKinnon took the snap, faked a handoff to receiver Brandon Aiyuk and was promptly tackled for a three-yard loss. It simultaneously moved the 49ers out of field goal range and removed going for it on fourth down from consideration. The 49ers then punted, and while they managed to pin the Seahawks down at their own 1-yard-line, the curious play call on third down was a major error they would soon regret.
After the loss, 49ers coach Kyle Shanahan defended the play in a vacuum, but explained that Seattle's defensive call ultimately spoiled any hope of success.
"I liked it when I drew it," Shanahan told reporters, "but the Seahawks had a zero blitz called and we had no chance."
Zero coverage refers to an all-out blitz. The Seahawks threw extra attention at the line of scrimmage and provided more pressure than the 49ers could block. McKinnon had nowhere to go with the football -- except for a wide-open Garoppolo on the right side of the field -- and a great opportunity was wasted.
Ironically, the 49ers had a chance to make up for their mistake on their very next possession, but Garoppolo threw a terrible interception in the red zone and the momentum swayed back in Seattle's favor. Seven plays later, the Seahawks scored a touchdown, and the 49ers were in catch-up mode the rest of the day.
The third-and-5 call happened early, but it had a huge impact on the outcome. It might be a great play in concept, but there's no question it was the wrong one for that situation.