Answering the Fantasy Football Players Injury Dilemma
All fantasy football players have had this dilemma:
Player X is my best option at WR 2 but he’s coming off of that groin injury and took limited reps in practice this week… should I start him or go with my backup who averages a couple less points?
The real question being asked is: what effect does being on the injury report have on average weekly performance when a player is still active for game day?
To analyze this question in an objective way, we need to look at the numbers. Specifically - we need to contrast the average or expected output of Player X when healthy (defined here as not-listed on injury report or full-participant in weekly practice) vs average or expected output of Player X when injured (defined here as listed on official injury report for the week and/or limited practice reps). But Player X is a pretty small sample size so lets aggregate the differences across the league by position and injury type. The goal is to get a better overall understanding of whether certain positions are affected more by injuries, or if certain types of injuries have a more noticeable impact on fantasy football performance.
For this information - I downloaded the full offensive stat list for each team from fantasydata.com and grabbed what I could for injury report data from nfl.com/injuries which, unfortunately, was limited to the 2017 season only. As you'll see from the data, even an entire NFL season boils down to a pretty small sample size but there are still relevant insights to be gained.
The criteria which we used for the analysis is as follows:
Hurt: Injury listed on injury report but player active and took snaps in game
Healthy: Full practice participant with no injury specified, or not listed at all on injury report
Aggregated by player average points (standard league) when healthy vs player average points when hurt. (weeks that a player left game early and did not return the following week were removed so as not to distort the ‘healthy’ averages)
Since different players obviously average different hauls in points, we need to look at the average difference in points, isolated by player. We can then combine these across the league by position group and injury type to get a better look at the overall picture.
I’m working on creating an unbiased metric for opposing defenses so that we can more fairly drill down to how different injuries may affect specific players, however for now this will serve as a good overall indicator in the average change in production (points) between healthy vs hurt - as it would be highly improbable that all weeks when players ‘played hurt’ aligned with weaker defenses and/or all weeks when players ‘played healthy’ aligned with better ones (or vice versa).
You might have noticed that I refrained from using the word ‘drop’ or ‘decrease’ when referencing the average change week-to-week when healthy vs. hurt … and the reason for that is the available evidence is inconclusive that you should expect any change as long as said player is listed as active.
The overall distribution is pretty normal (both positive and negative) and most of the data are well within the standard margin of error week to week for each position type (about 4.18 points overall). Additionally, in most cases the higher frequency injuries (larger sample size) were closer to the healthy averages when aggregated - meaning there’s a correlation between less data and a greater deviation from the norm, and vice versa.
Avg Standard Deviation of weekly Fantasy Points by position: (Standard League, from this dataset)
QB +- 6.49
RB +- 4.64
TE +- 3.08
WR +- 4.01
This further suggests that the more extreme deviations (in the data) may just be one-offs. In fact every data point outside of the 4-point margin had only 1 or 2 occurrences in 2017 to draw from and probably don’t qualify as hard evidence of any trends.
I think that may be interesting in and of itself. This suggests that there shouldn’t be any expected change in production as long as a player is active. This also makes sense from the team’s standpoint, if you consider that by the time they allow a player to participate on gameday they expect his performance to be close-to-par. We also know that essentially every player is ‘hurting’ somewhere (from normal wear-and-tear) so ‘playing hurt’, as defined here, may be closer to the norm than most fans realize.
The net was about a 0.40 point overall reduction on average, but again with plenty of examples where players performed better than normal. It’s certainly not conclusive, however, and would be very interesting to see if this holds true over a 10 year period or more - or if the NFL has gotten better over time at diagnosing when a player is ready to come back.
Avg Change in Standard League Points (Healthy -> Inj) by Position, 2017 season
Avg Change in Standard League Points (Healthy -> Inj) by Injury, 2017 season
Stay tuned for the other side of this as we take a look at defensive players in a future post. One thing I’m curious of is the potential case that offenses attack a defensive player (or his side of the field) more often when they are known to be injured - which may lead to an increase in opportunities to make plays and accumulate points.
For reference, here is a link to the NFL’s official personnel injury report policy for the 2017 season.