Where does the value go when an NFL line moves?
Jul 20th, 2011 - Posted by Andrew_Brocker in American Sports
bettingexpert blog editor. Always taking the alternative route to finding the value.
Twitter: @AndrewBexpert
Is there still value in a NFL betting line once the line has moved? Which side of the line should we look to after there has been a significant shift? Andrew breaks down the last 10 seasons of NFL games in an attempt to answer the question and see if there are any trends to keep an eye on.
Over the last 10 seasons, 75% of NFL games have seen the betting line shift in one direction or the other, moving from the opening line posted early that week. More often than not it's a minimal shift. Perhaps half a point.
In fact line moves of half a point constituted 40% of all line moves the last 10 seasons, with line moves of a whole point making up 24% of all line moves through that span. Together, that accounts for almost two-thirds of all the NFL games saw a move in the betting line the last 10 seasons.
NFL betting lines can move quick, with smart Vegas money swooping in to take advantage of lines they believe are off the mark. And they can move dramatically.
So what happens when a line moves more than a whole point? What happens to the value when a line bolts upwards of 2, 2 and a half points or greater?
As usual, curiosity got the better of me and I decided to sit down and get kinky with my NFL spread sheets and databases and try to determine where the value goes when an NFL betting line shifts.
Is there still value when a line moves greater than 2 or 3 points? What about when a line moves in a particular direction? Home teams? Road teams? Favourites? Dogs?
I analysed Las Vegas casino opening and closing lines the last 10 seasons. This is what I found out.
Oh and I've thrown in an analysis of Over-Under line moves. Just because I am obsessive.
Home Teams Firming
Ok, so let's start with a simple breakdown. Here we will look at basic line movements in the direction of the home team. We'll call this Home Teams Firming. (Or HTF for those of you who are into the “brevity thing”.) For example, a home team's line moving out from -7 to -9 is a home team firming by 2 points. Or moving in from +5 to +3.5 is a home team firming by 1.5 points.
So what do we see here? Well, overall, not much.
When home teams firm by any degree the last 10 seasons, they are 50.25% against the line. (For here on, ATL).
But when a line shifts by at least 1.5 points in the direction of the home team, home teams are 171-150-13 ATL. That's 53.1%.
Sure, paying standard bookmaker commission, you're not going to be walking away with a handsome profit at 53.1%, but it says something for the belief that once a line moves, the value drains.
And if we took all home teams that assumed a line firming of 2 points or more the last 10 seasons, that record betters to 98-83-9. Or 53.9%.
If we go a step further and eliminate violent line shifts of 4 points or more, that record stands 90-73-8. That's just under 55%. Sure, we're doing some Captain Hindsight record crafting here (and you know how much I hate that) but the point to take away is that don't be spooked against taking a team even when the line has run out in their direction.
Road Teams Firming
So now let's turn to Road teams. And when road team's firm.
Do we see much to take note of here?
Well overall, we see road teams firming are 50.75%. Ok.
If we look at line moves in the direction of away clubs by 3 or more points, the record is 44-34-1. That's 56.3%.
Yeah, it's only a sample size of 79, so perhaps we should tread with caution, but again, there is value in lines even with such a significant shift from the opening number.
Home Favourites Firming
Ok, so now let's break it down a little further and see what we find. And let's make our analysis a little (yes, just a little) more sophisticated.
Here we will be looking at home teams that are favourites when the opening line is posted. And where the number has moved in their direction. So from -3 to -6 for example.
Further, we won't just be looking a simple half point shifts in the line. We will look at the overall shift as a percentage of the opening line posted.
Why? Well, because a line movement from let's say -3 to -6, is more significant than a 3 point movement from -13 to -16.
So it works like this: a move from -3 to -6 is a shift of 3 points, which is 100% of the opening -3 line. Or for another example, a move from -7 to – 9 of 2 points, is a shift of 29% of the opening line.
Overall we see that betting against home favourites that have taken a line move in their direction are 52.1%.
And if we bet against home favourites in this situation where the line has shifted at least 100% of the opening line, the record is 19-12 -2 or 60.6%.
Again, it's a small sample size, so perhaps we shouldn't take too much from it. But overall, it appears that the value trends a little towards the road team when a home favourite gives a line shift of any number.
Home Favourites Drifting
Now let's look at when opening line home favourites come in. For example, moving from -4 to -1. Simple enough.
Overall, there isn't much to take notice of.
But when we see the line move at least 30% of the opening line in the direction of the road dog, the record for home favourites is 88-72-2, or 54.9%.
And if we elminate violent line changes of greater than 200% of the opening line, the record improves to 72-56-2, which is a handsome 56.2%.
Again, we don't want to start 'juking the stats' too much, but overall, in this situation, where home favourites drop points, the value at the closing line appears to be with those home favourites.
Home Underdogs Firming
Let's turn to home dogs now and in particular, when home underdogs firm in price, say firming from +6 to +4 for example.
This is where we see our most stark trend. Overall, home underdogs firming at the line are 55.1% the last 10 seasons. That's on any line movement at all.
Below line shifts of 40%, the record is 113-96-6, just under 54%.
But above 40%, the record is a very attractive 45-32-3. That's 58.1% the last 10 seasons.
So it seems that as we go into the 2011 NFL season, that we should keep an eye on home underdogs who have firmed in price from the opening line.
Home Underdogs Drifting
So let's conclude our head to head line analysis by looking at home dogs who have drop at the line. We're talking about teams drifting from +3 to +4 for example.
Not much to take notice of overall. Its roughly 50% either way.
But when we look at line moves of at least 80% of the opening line, we find a nice trend for home dogs of 22-13-2. That's 62.2%.
I would be hesitant to read to much into a sample size of 37 over a 10 year span, but still, perhaps keep an eye on home underdogs this season who have taken points over 80% of the opening line.
Over/Under Line Rising
Ok now let's turn to some Over/Under analysis. Here we will look at the line change from the opening Over/Under number as a percentage of that opening number. So for example, a shift from 40 points to 42 points, a 2 point rise, is a rising line shift of 5% of the opening number.
First we will look at where the value trends when the Over/Under total rises from it's opening post.
Overall we don't see much. In fact when the O/U number rises, the value trends slightly towards the under. About 51.1% the last 10 seasons.
But when we get above a lifting line of 6% or more, that record becomes a nice 37-25-2 for the Over. That's 59.4%. Sure it's again a small sample. But perhaps keep an eye on significant lifts in the O/U line this upcoming season.
Over/Under Line Dropping
Lastly, we will look at what happens to the value when the Over/Under line drops.
Overall, we see a relatively healthy trend towards the Under whenever a O/U line drops of any range. The last 10 seasons, the Under has been 51.2% in this situation.
But when we look at significant shifts we see some interesting numbers.
When the Over/Under total drops at least 4% of its opening number, the Under improves to a record of 180-148-11, or 54.7%. And that's a sample size of 339 games.
And if we look at drops of 6% or more, the Under record is 69-54-3. Just under 56%.
So the lesson here is, don't be too spooked out of taking the Under, even when the O/U number drops.
So what did we learn?
In conclusion, here's a few key points to keep in mind when considering your NFL lines this season.
- We should consider home favourites drifting
- We should strongly consider home underdogs firming
- We should strongly consider the Under when the number drops.
You can follow Andrew on Twitter @AndrewBexpert
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How about some NBA stats similar to these?
I'd love to do a similar analysis for football but don't have that sort of odds shifting data for football handy. I'll have a snoop around and see if I can get my hands on some
Brilliant work Andrew, really like the way you break things down any chance on something similiar for the football like what happened with the odds for that pick earlier.. Cheers.....
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I do have that data for the last 7 NBA seasons. I'll put it on my list of articles-to-do Rafrochen. Thanks for the suggestion