Kyle Shanahan explains why Nick Mullens snapped the ball too soon on kneel-down vs. Broncos

San Francisco 49ers quarterback Nick Mullens snapped the football prematurely on what should have been a game-winning kneel-down on Sunday against the Denver Broncos. It left Denver with seconds on the clock and one last shot to win the game.

Mullens vows that something like that won't happen again.

"I shouldn't have done it in the first place," he told reporters after the game.

Head coach Kyle Shanahan spoke with the media on Wednesday and shed some light on what actually led up to the offensive miscue.

It turns out Mullens lost track of what down it was.

"I don't think it's a big deal because we won now," Shanahan said. "It would have been a huge deal (had we lost). You've got to measure it out with the time and stuff. We can all add. I asked someone else to do it in the heat of battle, just so I don't mess it up. But it was very easy. We could kneel it out.

"On second down, he kneeled it with like five seconds instead of at one, which was the first lesson for him to learn. When we did that, it went down. You could see on the play clock, it's at 18 seconds, but on the game clock, there's 19. So you know there's a second that you have to gain there. We shouldn't of, but kneeled it like four seconds early.

"So, that happened, and we're realizing that when it's third down, and everyone's headsets are off, which I'll never take mine off again.

"But the headsets are off, and we're all hugging and stuff. Then someone tells me, so I yell to Nick, 'Hey, you need a slow knee!' That's something we go through. It's when you've got to step back and kill a second before you take a knee. And I'm yelling it because I'm a little panicked.

"Nick, very calm, just hushes me and tells me to chill out. So I'm like, 'Alright, he's got it.' So he was relaxed, and he snapped it. He did exactly what he was supposed to do, did a slow knee. It took almost two seconds (off the clock) before he did it.

"The problem was, when we were telling him that, he's not thinking much. You tell him, and he looked right up at the scoreboard, and you can see it on tape, the scoreboard says 3rd-and-12. It's (actually) 4th-and-12.

"He was like, 'Alright. I don't know why Kyle's freaking out. Slow knee? I'll do a slow knee.' But he snapped it with five seconds on the play clock thinking he was going to be able to do it again on 4th-down, but that was 4th-down.

"So he lost track of the downs, just like Tom Brady this week lost track of whether they had a timeout left or not. It does happen. I wish I was on that so I could have had him go through the whole thing. But it's a good learning lesson for him that you snap it at one second no matter what, that you don't always pay attention to the scoreboard because they're not always on it, and that your coach should never take his headset off."