I think that if Davis starts on Sunday and continues to start all while gaining experience and confidence. ....it is very possible that neither Hill or Keenum get a chance again this year. However if Hill goes back into the starting line up this week or next then it is possible that Keenum will leapfrog Davis on the depth chart and get his chance if Hill struggles or is hurt again. But I believe Fisher when he said Keenum was brought in as depth behind Hill. I guess my thoughts are that right now there is NO competition for the starting QB job..... it is Hills..... however if Hill can't go this weekend and maybe even next..... then this is a prime chance for Davis to enter the argument. Remember Davis had his first regular season snaps..... passes ...and completions in his career last week. If he starts this week..... shows poise ( because the game is slowing down). .. knowledge of the offense and moves them up and down the field...it will be hard to get him out of there.....just my thoughts. ..... Go Rams.... 
