There is a certain mystery about how bookmakers set lines for NFL games that varies from sportsbook to sportsbook. There is no position more important to a line than a team's starting quarterback.
For oddsmakers, it is a constant challenge to keep track of injury reports, coaches' news conferences, Twitter and more to figure out starting QBs each week and adjust spreads accordingly.
When a QB change is made, how do oddsmakers adjust? How much is each quarterback worth against the point spread?
The answer to this question is nuanced and involves a quarterback's overall talent level, how much better he is than his backup and where the difference between QBs lands with respect to key numbers (three, four, seven, etc.