The 49ers’ 13-3 loss to the Seattle Seahawks was their third game in 13 days, but coach Kyle Shanahan believes that’s not an excuse for the overabundance of missed tackles by the defense on Saturday. 

“Yeah, that definitely doesn’t make it easier,” Shanahan said on Monday via conference call. “I think that stuff adds up. I think it does with injuries and stuff, too, but that can’t be your excuse for it. I mean, that’s just stuff that doesn’t make it easier. 

“You’ve got to find a way to do it. We said it during the game and it’s only more evident after, 18 missed tackles were way too much.”

The missed tackles gave way to 180 yards on the ground made by the Seahawks — the most the 49ers allowed this season — and another 181 through the air by former San Francisco backup quarterback Sam Darnold. But one play in particular clearly broke the spirit of Robert Saleh‘s defense. 

With a little more than four minutes left in the third quarter, Darnold fumbled a handoff to Zach Charbonnet for a loss of seven. On the ensuing play, linebacker Tatum Bethune broke up a pass intended for Seattle tight end AJ Barner. 

In that third-and-17 situation, Kenneth Walker III took the handoff from Darnold and ran the ball 19 yards through several 49ers defenders for a first down. It was a well-designed play by Seattle, but it also appeared like the 49ers’ defense was moving more slowly than their opponents, with multiple missed tackles on the play.

“[It] just tracks their top speed and how much yardage they cover in a game,” Shanahan said of the GPS devices in players’ shoulder pads. “Our guys were, speed-wise, fine. They were same as the week before.”

Now the defense has the tough task of preparing for the No. 3-seeded Philadelphia Eagles in the first round of the NFC playoffs, and an equally lethal ground game led by All-Pro running back Saquon Barkley.

This time, the defense will be without Bethune, who suffered a season-ending groin injury in the loss.

But the extra day to rest, recoup and prepare should help the 49ers.

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