The premise is simple. You don`t care who wins or loses - all you care about is whether the total number of points scored by both teams together is more than a certain number or less than a certain number. That 'certain number' is the NFL over under or total. Much like the point spread, oddsmakers set the total and invite you bet over or under.
For example, if the Giants vs Cowboys game has an over under value of 45.5 and the final score is 30-17, then OVER bettors win (because 30+17 = 47 which is greater than 45.5). If the final had been 27-17, then UNDER bettors would win because 44 is less than 45.5.
So much for thinking that missed field goal was meaningless, huh? It may have been meaningless to the game, but not to the football total. Hence the reason why every play is important to a football bettors, even after the game is out of hand and it's obvious that one team will win.
Handicapping NFL over unders requires consideration of many of the same principles as point spread wagering. Knowing key offensive and defensive stats is important, knowing coaching philosophies and game plans and knowing the weather are all important factors in determining whether the game will be high-scoring or low-scoring.
NOTE: only available in the Wins pools, N/A in Confidence Pools