How do sportsbooks set 2nd half lines? Specifically football and basketball.

[SparJMU]

I play a ton of 2H lines in the NFL, NCAAF, and NBA. Still, I don't fully understand the markets and have some questions. I am curious to know how sportsbooks set their 2nd half lines. Is there a set of formulas that determines the 2H spread based on the full game spread, and the score at halftime? For example, I have noticed that when favorites are behind at halftime, they are almost always favored in the 2H as well, regardless of how poorly they are outmatched on that day.

Are there actual sportsbook employees who watch the game and adjust 2H spreads based on the results of the first half? I have made some huge 2H plays when there have been key injuries in the first half, and I don't believe the sportsbooks have adjusted their 2H line accordingly.

Also, I have noticed that 2H spreads change very quickly, which makes me believe the sportsbooks really aren't very good at setting these lines, and they adjust quickly based on sharp action. Is that assumption correct?

I appreciate any wisdom the experts can share on this subject.

[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.

[Pancho sanza]

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.

You lost me here:

"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."

Can you expand your answer?

thanks

[Peregrine Stoop]

2nd half spread before game + reversion to the mean based on first half result + injuries/foul issues/etc from 1st half

[SparJMU]

Pancho, what he means is to pay attention to the key numbers that you would already suspect in football. For example if a small favorite is up 3 at the half, a 2H line of 0 is now a very key number because it leads to a full game key number of 3. There is a huge difference between the favorite being a PK in the 2nd half and +0.5 in the 2nd half because this is in essence a full game -3 versus a full game -2.5.

Still unsure of one issue though....why lines move so quickly at halftime? Do the books know that their lines are weak and therefore they adjust quickly even on light action? Or do you think there are "sharps" who are placing significant bets, causing the books to adjust their lines quickly?

[Pancho sanza]

Pancho, what he means is to pay attention to the key numbers that you would already suspect in football. For example if a small favorite is up 3 at the half, a 2H line of 0 is now a very key number because it leads to a full game key number of 3. There is a huge difference between the favorite being a PK in the 2nd half and +0.5 in the 2nd half because this is in essence a full game -3 versus a full game -2.5.

Still unsure of one issue though....why lines move so quickly at halftime? Do the books know that their lines are weak and therefore they adjust quickly even on light action? Or do you think there are "sharps" who are placing significant bets, causing the books to adjust their lines quickly?

I agree with that part, about a 3 point lead at half in foorball, but not about 1 and 6 being key #'s

Also the part about a small fav up 8 in baskets etc, dont agree with that.

[$tinky]

they move so quickly and so much because of the amount of time they take action on the contest. Think about it. A Full game has a weeks worth of time for bettors to bet lines movers to adjust. a 2h has about 5 or 10 minutes. So a bet gets much more attention.