Originally Posted by
Justin7
The baseline is *roughly* game spread x .60 for the first half, and game spread x 0.40 for the second half.
Then, they adjust the second half spread based on the score. If the favorite is up 60% of its spread (i.e. a 10-point favorite is up 6 at half), the second half line will be pretty close to 40% of the game spread (or -4). If the favorite is ahead of pace, the line moves towards 0. If the favorite is behind pace (i.e. tied at half), the spread moves up.
Two quick thoughts: First, injuries or weird situations can adjust the line. These are often overlooked. If Aaron Rodgers has a concussion in the first half, the fair game line is no longer Fav -10. Second, certain numbers are more significant, or are dead. If a 4-point favorite in NFL is down 3 at half-time, betting it at -2.5, -3 or -3.5 are virtually the same (unless the game ties in OT). Getting +0.5 points in a "stable" score (i.e. small fav up 3 in nfl, or small fav up 8 in baskets) can be worth a lot... 1, 3, 6 and 7 hit pretty often in football. The score changes the value of different numbers though.