A "mobile quarterback" refers to a football player who is able to run quickly and move around the field easily while still being able to throw and pass the ball. Full definition
Like a lot of mobile quarterbacks, Knighten is sack prone. (sbnation.com)
With that being said, the Patriots have had trouble with mobile quarterbacks in the past. (sportsinsights.com)
Given his offensive expertise, and given that he almost coached the most mobile quarterback ever and that he's acknowledging you needed then - unseen level of speed at the QB position to get around the edge on reads, I can't not ask. (sbnation.com)