Chicago Bears – 1986
The Bears went 15-1 in 1985 and won the Super Bowl. It appeared that a dynasty had begun but the truth was very different. The following year they became a one-and-done playoff team as they failed to defend their title. This wasn’t the way they expected to fall out of contention.

Chicago only allowed a record low of 186 points all year. But Jay Schroeder unlocked their defense and threw a couple of key touchdown passes. The Bears couldn’t mount a response and the game drifted away from them. It was a shocking loss but no less than they deserved (via Bleacher Report).