The Problems with Value-Based Drafting
Value Based Drafting in fantasy football is essentially valuing a player to the extent he exceeds the baseline player at his particular position. For example, if Aaron Rodgers is projected to score 427 fantasy points, and in your 12-team league, the No. 12 QB (the baseline player), Robert Griffin, is projected to score 322 points, then Rodgers' value is 105 points. Compare that to Adrian Peterson who we project for 290 points and who exceeds our No. 24 RB, Ahmad Bradshaw (168 points), by 122 points. According to VBD*, Peterson is more valuable than Rodgers in that case - by 17 points.
*Not all VBD systems use the worst projected starter as their baseline player.
The advantage of VBD is it allows us to compare players across positions. But it has several problems:
(1) It's hard to determine the real baseline for a given position.
It's easy to use RGIII as the baseline QB, but given his injury and playing style, most people probably have him projected for only 13-15 games. As such, if you were to draft him, you'd likely get 14 games of RGIII plus two other games of the No. 20 QB, or whomever you managed to pick up that week. Michael Vick presents a similar problem. Moreover, what about the owner who drafts Eli Manning and Philip Rivers and plays only optimal matchups? Or the one who hits the waiver wire and mixes and matches every week? On the downside, some owners will get burned playing matchups, and others will see their signal callers injured in the first quarter in some games. In sum, the baseline is a moving target and so the No. 12 QB's projected line might not be a good stand-in for it.
(2) It's unclear whether No. 12 QB/No. 24 RB is really the right level in any event.
For the No. 12 QB to be the real baseline in a 12-team league, you'd have to have a rule that you draft your entire starting lineup before filling out your bench. That way, if you pass on Rodgers early, you'd know the No. 12 QB (Griffin) will be there for your last pick. If you pass on Peterson or some other RB for Rodgers, you know Bradshaw will be there with your last pick. Of course, it doesn't work that way. People double up on QBs all the time, or take five RBs. By passing on a player at a given position, you're by no means guaranteed the No. 12 or No. 24 player there. While the last-ranked starter is a rough approximation of positional depth, it's far from perfect. For example, if RB really drops off terribly after pick No. 30, and people triple up on backs early in the draft, the price for taking Rodgers over Peterson early is certainly steeper than 17 points, so long as good QBs are around.
So what is replacement value, i.e., the baseline player, in a given league? That depends on bench size, roster requirements and owner management styles among other things. The most accurate way to get a sense of it would be to look over the league results the last five years and see what each owner got from each *slot*. The worst starting RB slot on average might be considered the baseline. Same with QB slot. Not individual players but what the owner got from his slot. This isn't easy to do because most commish services don't track individual RB slots, and most owners randomly move their players around between eligible slots. Finally, the FLEX spot(s) complicate this kind of calculation enormously.
(3) VBD doesn't take into account market perceptions
Even if we were able to figure out the proper baselines with some precision and therefore had a good idea of how players should be valued based on their projected production, we also have to account for the perception of players' value - no matter how erroneous - by the rest of our league. For example, if you're in a league where owners overvalue quarterbacks, there might be better running backs available in the later rounds than there should be. In that case, you pay a steeper price in QB quality for passing on Rodgers in Round 1 and a less severe one for passing on Peterson than you would in a normal league. If David Wilson is available in Round 6 and Lamar Miller in Round 8, waiting on running backs suddenly makes a lot more sense. While that might sound like an extreme case, leagues do vary widely in the way they value quarterbacks and running backs even with identical scoring systems.
(4) Projected stats don't take volatility into account
When you're making your VBD calculation, you're looking at a single projected stat line translated into fantasy points. But Rodgers' 427 points isn't the same thing as Peterson's 290. The quarterback projection is more reliable as Rodgers is less likely to miss time with injuries than a workhorse running back and less dependent on his team's play. In fact, the quarterback determines the team's play to such a large extent that an elite quarterback is almost assured of being in an elite offense, whereas an elite running back needs to get his red-zone looks based on the team. In Peterson's case last year it didn't matter much because he carried the offense on his back, but even for great running backs that's the exception more than the rule. If Rodgers' 105 points above the baseline is more of a sure thing than Peterson's 122, shouldn't that carry extra weight? Especially early in the draft where you want to minimize volatility and maximize consistency?
In sum, VBD isn't a bad place to start when doing your overall fantasy football rankings, but it's far from precise, so it's important to take into account nuances of your league like bench size and owner tendencies and also adjust it for volatility.