For the Denver Broncos, the defense was not entirely the weak point. But there were some holes. As far as a complete unit, the Broncos run defense had some solid moments, but also were victim to some bad games. One game that stands out to me is week four against the Jacksonville Jaguars.
There is no doubt the team needs to get better at stopping the running game. When games get into the colder months, there is more emphasis on running the rock. It keeps the game clock running and therefore less time to get a comeback if that is what is needed.