I think that the Broncos are going to be undefeated this season because they have done so great up to now. The Broncos may have a little bit of a competition going against the Kansas City Chiefs twice. The Chiefs may figure them out, but Denver will still beat them. Peyton Manning is like the general of the team and leads his players to victory. His leadership is also very helpful to inspire the rest of the team and has brought a new attitude for even the defense. The only way that the Broncos could be defeated is if injuries become problem. Many teams have had problems with injuries, but if the Broncos stay healthy they will be able to beat any other team.
The Broncos defense will have to work hard to be on the same level as the offense with Peyton Manning. If Manning can stay healthy and the defense can hold the points to a minimum, then there should be no reason that the Broncos won't be undefeated this year.