Goff I believe has been banged up some and Hooker the backup is a rookie I believe I think with them thinking its Super Bowl or Bust they don't want a backup rookie possibly thrust into the limelight. Bridgewater as a veteran just has a much better grasp of the game 

Has Goff or his backup been injured? Seems kind of odd to add a QB now unless they are concerned about one of the other guys. 

grayruby

Sounds like he will be the primary backup to Goff! I could see him being a 3rd stringer for a week or so as he gets in shape and full up to speed but he did play for the Lions last year so he knows the playbook!