On May 10, 2014, Underwood was signed as an undrafted free agent by the San Diego Chargers. On August 30, 2014, he was waived. On September 3, 2014, Underwood was signed to the Philadelphia Eagles' practice squad. On September 9, 2014, he was released from practice squad.
On September 23, 2014, Underwood returned to the Chargers and was signed to their practice squad. On December 29, 2014, he signed a future contract. On September 5, 2015, he was waived. On September 6, 2015, he was placed on injured reserve. On September 10, 2015, he was waived from injured reserve.