Understanding the importance of backups in best ball fantasy football

• Understanding “marginal contribution”: If a backup quarterback in best ball were to outscore the starter in five of 17 games by a combined 40 fantasy points, that is their marginal contribution to your team.

• Projecting marginal contribution: Using fantasy football projections, we can predict how valuable each backup is to the starter or starters on your team, thus helping you draft more efficiently.

• Other best ball factors: We also examine bye weeks, strength of schedule and upside to better understand the value of backups in best ball fantasy football.

Estimated Reading Time: 12 minutes

Best ball fantasy football is a format without weekly roster management. The best possible lineup from your pool of players is chosen each week. For example, if you’re in a league with two starting running backs and you have four running backs on your roster, the two highest-scoring running backs are chosen as your starters each week in a posteriori way.

This format has a few consequences:

Every decision that leads to you winning your league has to be made right now, during draft season.
Backups play a much larger role than in classic re-draft leagues, as there are technically no backups in a classical sense. There are just players who are expected to be automatically chosen as a starter more often and players who are expected to be automatically chosen as a starter less often.

From a predictive standpoint during your fantasy draft, the rate of how often a player is ultimately expected to contribute to your team as a starter depends on different things:

Their fantasy points projection going into the season
The number of starters in the league at their position
The quality and quantity of competition in your own team — i.e., how many players at the same position do you own and how many fantasy points are they projected to score?

We want to quantify the combination of these factors to help you make the best draft decisions.

Marginal contribution

Say you already drafted Josh Allen in a one-quarterback league and you’re currently faced with the question of whether to draft Matthew Stafford as a backup quarterback (or rather, your second potential starting quarterback). What’s the value of drafting Stafford?

For the moment, let’s forget about any sort of injury concerns and just look at the projections of these two quarterbacks. We currently project Stafford to score 254 fantasy points in the 2023 regular season. Obviously, Stafford won’t contribute 254 fantasy points for your best ball team, as he competes with Josh Allen — who is projected to score 365 fantasy points — for the lone starting spot at quarterback.

Going one step further means projecting how often Stafford would outscore Allen on a weekly basis. Let’s say we project that to happen five out of 17 times (it’s obviously less than 50% of the time, because Allen is supposed to be better). Stafford’s 254 fantasy points translate to about 15 points per game, so he would be projected to score 75 points in five games. Is this number equal to Stafford’s contribution?

The answer is a clear no. This is where we realize that things are too complicated to be computed by hand: First of all, Stafford will score more than 15 points per game when filtering to the weeks where he outscores Allen. Secondly, Stafford’s value isn’t defined by how many total points he scores in weeks where he outscores Allen; it’s actually defined by how many points he scores over Allen in those weeks. After all, the alternative is passing on Stafford and taking what Allen gives you every week.

For example, if Stafford outscores Allen five times and scores 110 points in these games while Allen scored 70 points in these five games (that sounds low for five games of Allen, but note that one of these five games will be Allen’s bye week), Stafford’s value to your team is 40 points. We call this number his marginal contribution.

To predict the marginal contribution of Stafford over Allen, we run simulations. Using a nearest-neighbor approach (looking at past weekly fantasy results of quarterbacks with similar season-long fantasy points), we estimate the weekly distribution of both quarterbacks.