If you play in a fantasy football league that uses the flex position, the draft is a race to fill that spot. In other words, that added roster spot encourages owners to load up on wide receivers and running backs early and often (even if you can flex a tight end, it’s almost never a viable strategy). Once the season has started, deciding who to put in that flex position can be a weekly struggle, especially because it is so difficult to compare running backs to wide receivers in an apples-to-apples manner.
In almost every case of rostering your flex, using John Paulsen’s flex rankings at 4for4 will suffice—just plug in the higher ranked player. There are instances, though, where a running back and wide receiver are projected so closely together that deciding which one to plug into the flex can leave you pulling out your hair before kickoff.
Historical data can help point you in the right direction.
Choosing a Flex in Standard Leagues
Unless you loaded up on one position early in your draft or were fortunate enough for one of your late-round picks to rise to fantasy starter status, you’re usually choosing between a running back and wide receiver in the 25-to-48 range in their respective positional rankings when deciding on your flex every week (assuming a league that starts two running backs, two or three wide receivers, and a flex). By using 4for4’s Fantasy Points Browser, we can see how, using end-of-season rankings, RB3s and RB4s have compared to WR3s and WR4s in recent standard scoring leagues.
Average Standard Fantasy Points Per Game, 2013-2017
On an average per-game basis, running backs in the 25-to-48 range have scored slightly more than wide receivers in the same range in standard leagues. The margin has been so thin, though, that it’s worth comparing the positions at each individual ranking to look for more telling trends:
This visual representation highlights some interesting points to ponder when considering who to start in your flex spot in standard leagues.
Running backs in the 25-to-30 range have scored notably more than wide receivers in the same range in recent years. On a weekly level, most NFL teams still have one NFL back that dominates touches, which explains why we see the gap in scoring in this range.
After the top 30 backs and receivers, scoring between the two positions starts to converge. Backs who aren’t seeing starter-level touches are less reliable, while more receivers have a chance to affect the game.
Consider the opportunity for playing time. In any given week, there are only 32 running backs who have a chance at playing the majority of their team’s offensive snaps, while there are conceivably 64 receivers who can play virtually every snap. That added playing time for lower-end receivers is highlighted in the graphic. Low-end WR4s score more than low-end RB4s, even in standard scoring. When you are that low in the running back rankings, there likely aren’t enough touches available to make any running back a feasible starting option.
Choosing a Flex in PPR Leagues
The Fantasy Points Browser can also highlight how running backs and wide receivers who are likely to fill the flex performed over the last five years in PPR formats. From 2013 through 2017, WR3s and WR4s have outscored running backs in the same range. In fact, WR4s as a group have scored more than RB3s in PPR formats over the last five seasons.
Average PPR Fantasy Points Per Game 2013-2017
A glance at the individual end-of-season point-per-game rankings for each position is even more telling:
In PPR leagues, mid-range wide receivers simply score more than running backs with a similar positional ranking. Targets and receptions are so valuable in PPR leagues that running backs who aren’t workhorses or heavily involved in the passing game are very difficult to justify as worthy starters in the flex.
Running backs, even the ones ranked outside the top 24, who are significactly involved in their team’s game plan have value in standard leagues, and often outscore their wide receiver counterparts, but that scoring margin can be thin. After the top-30 running backs, scoring between running backs and wide receivers is so close that the flex spot is usually a case-by-case decision. Once you start comparing low-end RB4s to low-end WR4s, wide receiver opportunity almost always beats that of running backs.
In PPR leagues, receivers dominate scoring. Filling the flex spot with a wideout that is a borderline starter can give you an advantage over your league mates every week.
No lineup decision should ever be made blindly in fantasy football, and that goes for choosing your flex, too. If you have a running back projected to outscore your receivers, he should fill your flex, even in PPR leagues. Historical trends can help shape our drafting tendencies and in-season roster management techniques, though, and those trends should be considered throughout the season.