How Spreads Work
A -6.5 favorite must win by 7+ to cover; a +6.5 underdog covers by losing by 6 or fewer, or winning outright. Both sides usually pay -110, with the extra 10 cents being the book's vig. Whole-number spreads can push, refunding stakes when the margin lands exactly on the line.
Key Numbers and the Hook
NFL games disproportionately end with margins of 3 and 7. Moving from +2.5 to +3.5 crosses the most common margin in football, which changes your win rate materially — that half-point 'hook' is worth paying up to 20 cents of juice for by most models.
Basketball margins are more evenly spread, so key numbers matter less; spread shopping there is about price, not number.
Shopping and Timing
Openers are softest; lines sharpen toward kickoff as professional money arrives. If you like a favorite, betting early often gets the best number. If you like a dog, waiting can add points as public money pushes the favorite's price.