Second-half betting lines have the shortest shelf life you will find in NFL options. If time and volume wagered move lines to a more efficient price, then second-half lines are the best when looking for inefficient markets. This makes these markets some of the most profitable for professional sports bettors to target, but recreational or newer players often overlook their value.
There is little commentary or touting of these markets due to the inability to produce or send information during the shortened time frame. Previous work has provided an initial framework for what the ideal approaches are to betting second-half lines. Let’s test these initial theories and then see if any new insight can be gained from further methods.
Our initial dataset of 2,671 games includes all regular season and playoff games since 2010. From that, we can see the influence of full game numbers on second-half lines. For spreads, the full game explains .55 of the variance for second-half spreads, according to the R-squared value. For totals, the R-squared is significantly higher at .80 when looking at how much influence the full game total has on the second-half number.
If you notice relevant information in game from injury situations, schematic adjustments or any variable that may not be priced into the market, it is best to think about how that affects the total, as opposed to the spread, when approaching halftime. The total has a much higher tendency to be anchored to the full game line with little to no adjustment coming from in-game variables. Typically, if a starting quarterback gets injured in the first half, the spread will have an adjustment — but that's often not factored into the total when second-half lines are posted.
After removing pushes from our dataset, we see that second-half favorites cover the second half spread only 43.5% of the time, making underdogs worthwhile to back. Let’s check on other popular theories to see if there is value in betting certain situations that arise with second-half lines.