ok, i think i get the basics? or tell me if im wrong. lets say the football spread for the colts or whoever is to win by 10. and at halftime they are up 7. so the book puts up whatever number they put up and you take the other side to hopefully win one of the sides. how often does the score fall right in between and you lose both bets? are there certain numbers in foots to avoid? how about baskets? thanks all.
You got the basics down.
Remember, sometimes the pre-game bet you had never had a chance to be recovered at halftime (i.e. you pick a fav at -10 but at halftime, the favorite is down, 17-7; the 2H line would most likely be -7.5 to -10 for the favorite for 2H). Sure, you can bet +10 on the underdog now, but why bother when you could lose both bets if the favorite wins by a couple, 24-27? Or vice versa, you bet on the favorite again to "win the game" (betting the -10 2H line when down by 10), but the favorite loses the entire game by 24 anyway.
Basically, totals would be a better focus if you want to try and middle some bets.
Getting something like Over 42.5 for the game and then at halftime, the score is already say.... 17-10 (27 pts; leaving 16 left to go to hit 43 or more). The books can't put up a line of 16 pts to "duplicate the game total line" so they usually would make a line of uhh... O/U 21.5 to 23, probably.
That could be a middle attempt of several points if choosing the Under 23.5 for 2H as an example. It's up to the person's level of risk tolerance whether to middle or not, but obviously a total middle of 7.5 (come to think of it, 8.5 if dealing with a possibility of 2-pt plays in the 2H) could be worth getting for perhaps 20-40% of your game bet.
I have much more in mind but will stop for now.
* CalvinTy