Why do NFL commentators say that the Broncos are the scariest team in the league?

Scary for everyone. The Broncos are the most inconsistent team in the NFL. At any given time they can score, or turn the ball over. I think that it's scary for everyone. Nobody knows what they are going to do, they are scary because if the Broncos show up and play to their potential, they can beat anyone on any given night. but if they don't show up they can be one of the worst teams in the NFL.