The 49ers lost a Monday night game in Denver on November 11, 1985, to fall to 5-5. They only managed three points off three trips to at least the Broncos 11. Most memorably, there was this field goal try near the end of the first half, as described by the Chronicle:
Ray Wersching was lining up to attempt a 19-yard field goal when a fan threw a snowball that splattered on the ground three feet in front of Matt Cavanaugh, the holder.
Cavanaugh, momentarily distracted, fumbled the snap. Wersching couldn’t attempt the kick, and the play ended with Cavanaugh heaving an incomplete pass over the head of his offensive line.
John Elway drove the Broncos down the field at the end of the game for a field goal by Rich Karlis to win it. Montana was 17 of 40 for his worst completion percentage game in the NFL, to that point anyway.