5 NFL backup QBs who outperformed starters feat. Nick Foles

The quarterbacks are the most important players in the entire NFL. Their individual output directly impacts their team's success as it has been proven many times in NFL history that an elite quarterback is capable of carrying a team. Conversely, a deficient quarterback can often hold back even the best of rosters.

When an NFL team has to play their back-up quarterback for one reason or another, it can sometimes derail a season completely. Other times, the back-up quarterback may come in and surprise everyone by outplaying the starter. Here are five examples of the latter type from NFL history.

#1 - Kurt Warner

When Trent Green suffered a season-ending knee injury during a preseason game ahead of the 1999 NFL season, most assumed the St. Louis Rams' season was over. The Rams would now have to rely on Kurt Warner, an unproven back-up with no great pedigree.

Warner shocked the world as he went on to become one of the greatest underdog stories of all time. He helped the Rams make two Super Bowl appearances and win a ring in one of them. He was named the NFL MVP twice during his legendary career on his way to the Hall of Fame.

#2 - Dak Prescott

While Tony Romo is one of the greatest quarterbacks in Dallas Cowboys history, he was unable to keep his job following a strong rookie performance by Dak Prescott.

Romo was expected to lead the Cowboys to be Super Bowl contenders during the 2016 season, as he had done before, but an early injury forced him to be sidelined.

Prescott was just a fourth-round draft pick and was considered more of a developmental project to potentially earn playing time in later years.

He was instead thrust into the starting role and immediately thrived, leading the Cowboys to a 13-3 record. Prescott was named the starter moving forward, so Romo decided to retire earlier than originally planned.