When a player goes down to injury in the NFL, taking advantage of the opportunity to find value can really set your lineups apart from others in both cash games and GPPs. There are a lot of key factors to consider when a player misses time due to an injury, so let's dive right in and take a look.
One important factor to consider is Snap Count. A player's snap count is determined by the percentage of total offensive plays each player in on the field for in a given game. Players who have a high snap count not only hold tremendous value for their team, but they generally hold significant value in DFS as well. Since these players are so valuable, when they fall victim to injury, there can be a substantial role that needs to be filled by a backup player.
Example: Arian Foster/Alfred Blue. In Weeks 1 and 2 of the 2014 season, Foster played 108 offensive snaps, while his backup, Alfred Blue, saw just 15 total offensive snaps, totaling 12 carries and 40 yards from scrimmage (5 of which came in the 4th quarter of Week 2, when the Texans held a substantial lead). When Foster missed Week 3 due to an injury, Blue stepped in and saw 33 offensive snaps, finishing with 14 total touches and 88 yards. Blue was minimum salary across nearly every DFS site in Week 3 and drew a great matchup against a Giants team that was 27th in the NFL against the run, according to Football Outsiders (FO). This is a prime example of a high-usage player (Foster) being replaced by a backup (Blue), who immediately steps into a sizable role in the team's offense. Why is this a great example? In 2014, Houston ran the ball on a higher percentage of plays (51.93%) than any other team. Because of this, targeting a backup RB in this situation will provide you with an instant source of value.
Each Situation is Unique
Another important thing to consider is that each situation is unique. Just because Alfred Blue made sense as a value play in this situation doesn't mean that every backup RB will be thrust into a significant role due to an injury to the starter.
The first example I provided was a RB, but these numbers can have an effect on other positions as well, but they are generally not as extreme. For instance, if a #1 wide receiver goes down to injury, it isn't nearly as likely that the next man up will be thrust into a substantial increase in usage like a running back might be. When you see a team's top receiver sitting out, you need to understand the difference in usage between a WR and a RB. Demariyus Thomas led the NFL in targets per game last season with 11.5, and there were only 11 other players who were targeted at least 9 times per game. Simply put, there is no guarantee that a team's #2 WR will see an increase in usage simply due to the #1 WR sitting out.
You will need to take into account the team's overall matchup when making your decisions regarding injuries to key players. When you do this, take a look at Las Vegas odds, snap counts, targets, and the opposing team's defensive numbers against the position. There are quite a few teams who have a significant difference between the strength of their run defense, passing defense, and overall defense. Just because a team has good numbers against the run or the pass doesn't necessarily mean that they are solid against the other. To give you an example from the 2014 season, the Washington Redskins ranked 9th in the league against the run, yet were dead last (32nd) against the pass and 30th overall, according to Football Outsiders. This means that they are an ideal target for opposing offenses overall, but not a great target for running backs. With that being said, you can often see teams whose numbers are skewed due to being so bad against either the run or pass that their opponents run less of one or the other in order to exploit a weakness.
When a player like Alfred Blue is thrust into a starting role in a good situation due to injury, they will be very high ownership percentage, especially in cash games. It is imperative to be aware of injuries and their potential impact so that you don't cheat yourself out of opportunity. When a player like this has a high ownership, you're immediately setting yourself behind the field by missing out, especially if the player involved is minimum salary. Be certain that you keep up with the most recent news and injuries in order to position yourself the best way that you can. This will have a long-term positive effect on your DFS success moving forward.