While playing an unfamiliar position in the biggest game of his life, Williams blundered.
"It is one of those things you have to take responsibility for, which I do," Williams said after the game.
But some people couldn't just leave it there and tweeted threats against Williams and his family.
"I'm irritated how people are treating him, absolutely," 49ers kicker David Akers said. "I think it's ridiculous. Get a grip on what life is about."
But it appears we have reached a stage in society where that seems impossible. Not since Columbian soccer player Andres Escobar kicked a ball into the wrong goal during the 1994 World Cup and was murdered, or Buffalo Bills placekicker Scott Norwood missed an easy game winner to lose the 1991 Super Bowl and went from hero to outcast, or Chicago Cubs fan Steve Bartman reached for the wrong foul ball, in the wrong place, at the wrong time and now lives in infamy.
"We've got some fans who are fanatics; I think it goes in the wrong direction sometimes," Jan Murphy said.
Murphy knows that better than most. Her brother is Billy Buckner, who booted a ground ball in the 1986 World Series, and suffered the collective blame of Boston fans for decades to follow.
She felt for Williams on Sunday.
"If you really got to know Williams, if you really get to know this person, he is just another human being," Murphy said. "We all make mistakes. But we are forgiven, where if you are a professional athlete, you are not always forgiven so easily."
Something to ponder as police guarded players at the 49ers facility Monday.
Twitter had no comment about the threats and at least one of the people who tweeted a threat to Williams has deleted his account.