Are NFL officials biased with their ball placement?
gutterstats.wordpress.comThis is actually true. But the numbers don't tell the entire story. Officials are trained to be biased towards a major yard line on change of possessions. Starting at a major line n these instances is insignificant to the drive. The upside being it is one less series where a measurement would ever be required.
It is a trade off of game flow (less measurements) vs a small inaccuracy where it doesn't matter.
Take a notice next game. A punt always gets spotted on a major yardline where possible. A punt inside the 10 of course would not be possible. Rounding from the 2 to the 5 would have a huge impact. Or if it lands and comes to rest directly between two major lines.
One item that I did not see discussed is the effect of penalties, which are generally made in 5, 10, and 15 yard increments. This combined with the relatively standard 20 yard start position could have an enhancing effect, or be an alternate explanation for the phenomenon.
ex: The offensive team starts from the standard 20 yard line. Then during the first play, a pass is made, and "block in the back" is called against the defensive team. The penalty would be 10 yards, and would put the offensive team at the 30 yard line for the start of the play.
This is discussed in the reddit comments. (It was my first thought to.) The weak consensus was that this is rare enough away from the 20 to not be enough to account for the data, which shows a similar bias toward 5-yard increments the entire length of the field. Further, there was an anecdotal report that NFL referee training specifically advises them to err toward a 5-yard increment in certain situations.
That is definitely true. If you want to measure ref bias, you should only consider plays in which the refs are in control of the spot (basically plays that end in a tackle being awarded).
There is also the flaw in that these measurements are reported by humans so we can't tell the source of any bias that might exist in the numbers. Similar to the glasses of water question in the lede, I think it is more likely that any bias comes on the reporting end rather than in the actual data. The refs don't spot the ball always on yard line so they might spot the ball at 38.4 yards. The person reporting that value is judging it by eye, so they will generally report that as on the 38 but will occasionally report it as being on the 39. Does the chance they report a ball that is at 39.4 yards as being on the 40 yard line increase in comparison?
This is cool!
Couple notes - 1. If 'normal' plays have a tendency towards a 10/20/30 yard line, what about plays where the ball placement is challenged? Don't know if your dataset has this, but under your framework, we'd expect to see a more even distribution of placements because of increased attention, though probably still with spikes at the 1 yard line and goalline. 2. Even though it's probably intuitive, the unimodal distribution of ball placements was cool to see.