According to OddsShark (h/t Gary Davenport of Bleacher Report), the eventual Super Bowl LII champion Philadelphia Eagles had 50-1 odds to win it all as of August 4, 2017. Remarkably, only eight teams were below them on the odds ledger.
Looking back at those odds, it's interesting to note successful teams that were not given much of a chance (e.g. the 150-1 Los Angeles Rams, the 100-1 Jacksonville Jaguars) and which losing squads were ranked higher (e.g. the 22-1 New York Giants, the 33-1 Tampa Bay Buccaneers).
Of course, it's easy to be a Monday morning quarterback and say the odds were off, but it shows that teams can always defy preseason expectations.