One of the biggest upsets in NFL history was Super Bowl III when the New York Jets defeated the heavily favored Baltimore Colts. No one thought the Jets had a chance, but Joe Namath guaranteed a victory and they pulled it off.
One more upset that comes to mind is the 1999 NFC Championship game when the St. Louis Rams beat the Tampa Bay Buccaneers. The Bucs had one of the best defenses in the league that year, but the Rams’ high-powered offense managed to score three touchdowns in the fourth quarter to win the game.
I have to mention the “Miracle at the Meadowlands” in 1978, when the Philadelphia Eagles stunned the New York Giants with an incredible comeback win. The Giants had a 17-point lead with just minutes left in the game, but the Eagles managed to score three touchdowns in the final five minutes to win the game 19-17.
Another big upset was the 1985 Chicago Bears beating the Miami Dolphins in Super Bowl XX. The Bears were favored, but they completely dominated the game with their famous “46” defense, holding the Dolphins to only 10 points.
One that comes to mind is the 2007 Super Bowl when the New York Giants beat the undefeated New England Patriots. The Patriots were a powerhouse team that year, but the Giants played incredible defense and pulled off the win.