1. Not having players prepared for the new overtime rules would get most coaches fired on the spot
The decision to receive makes little sense, but if the entire team was on the same page about it perhaps Shanahan should receive a pass. Hey, it's not what I would've done, but I'm not a head coach in the NFL. We've come to find out that the players had absolutely no idea what was going on.
The main job of a head coach is to put his team in the best position to win. There's only so much he can do from the sidelines, it's on the players to execute. But Shanahan is the one who put the game plan in place. He's the one in charge of making sure his team is ready for everything they can possibly encounter on the football field. The 49ers being unaware of how the new overtime rules work, as Lindsay Jones of The Ringer noted, falls squarely on his shoulders.
"Multiple San Francisco players said after the game that they were not aware that the overtime rules are different in the playoffs than they are in the regular season, and strategy discussions over how to handle the overtime period did not occur as a team. Defensive lineman Arik Armstead said he learned the details of the postseason rule when it was shown on the Allegiant Stadium jumbotron during a TV timeout after regulation. Fullback Kyle Juszczyk said he assumed the 49ers asked to receive when they won the toss because that’s what you do in the regular season, when a touchdown wins the game. 'I guess that’s not the case. I don’t really know the strategy,' Juszczyk said."
The Chiefs were fully prepared for the new-look overtime session, but Niners players had absolutely no idea what their coach was doing. Shanahan banking on there even being a third drive was one thing, but his players being unaware of what was going on and why Shanahan did what he did is simply inexcusable. Would it have changed the outcome? Maybe not. But the Niners being unprepared didn't help.