that about 80 percent of the money took us to cover at +15. Each half point usually means that there is a 15-20 percent trend.
So, say I'm a bookmaker. I open the spread at LSU -15. 20 people place $1000 bets, and only 4 take LSU. If LSU covers, I make a shitload - $16,000 in lost bets plus about $400 in juice. But if MSU covers, I only get about $4000 in lost bets and $1600 in juice, but have to pay out the $16,000 in won bets. Not good.
So I say lets move the line to LSU -14. I get an additional 20 bettors, with 10 people placing $1000 bets each way. This helps a little, if LSU covers the original 15, I still make a good amount, but if MSU covers, I'm still losing, but not near as much.
The bookmaker is trying to get as many people to take MSU as they do LSU, so I move the line to -12.5, this is where people start taking LSU. I get 20 additional bettors, with 16 placing $1000 bets on LSU and 4 placing $1000 bets on MSU.
I have $60,000 in bets on this game - $30,000 on LSU and $30000 on MSU. If the favorite covers the original spread or the underdog covers the final spread, I make $6,000 in juice. That's the minimum I am walking away with, and that's my goal as the bookmaker. If I wanted to make more money, I'd just bet on the game.