Expected to miss at least a week with a sprained shoulder, Buffalo Bills running back C.J. Spiller defied the odds and suited up last Sunday against the New England Patriots in a critical inter-division matchup.
Though that news initially delighted Spiller's fantasy owners, who assumed big-time work against a weak defense, the Buffalo back's presence quickly became the ultimate case of the gift and the curse.
Obviously not playing at 100 percent, Spiller grimaced on more than one occasion while carrying the ball just eight times for 33 yards, including a critical fumble on New England's 1-yard line at the end of the first half.
Though that possible touchdown would have salvaged his fantasy value for Week 4, it's become apparent Spiller's value is on the decline.
With a matchup against the San Francisco 49ers' vaunted defense on tap, it's likely that fantasy owners have no idea whether Spiller is a starter or should be better left on the bench.
Let's make one thing abundantly clear: In a perfect scenario, Spiller would be among the league's biggest breakout candidates for 2012.
According to Football Outsiders' advanced metrics, the 25-year-old speedster has been the best back in the league thus far, accumulating for 112 yards more than a replacement-level rusher would against similar opponents.
Nonetheless, it has become clear that the Bills seem married to the idea of at least a split between Spiller and Fred Jackson.
Starting for the first time since Week 1, Jackson got 12 carries, but was only able to manage 29 yards. Like Spiller, the elder Buffalo back looked nowhere near fully recovered from the knee injury that sidelined him during the youngster's ascent.
That means even the most optimistic expectations for the Bills' running game have to be split in some fashion. And since it's become relatively obvious that Spiller is the better of the two rushers at this point, we'll split the projections 60/40 in his favor.
Unfortunately for Spiller owners, however, splitting the yardage is unlikely to make much of a difference.
Coming into Week 5, the 49ers have the second-best run defense in the NFL, according to Football Outsiders' metrics. On average, San Francisco gives up 36.3 percent less yardage than an average defense would against similar running attacks.
For the Bills, that would mean taking their 158 rushing yards per game and subtracting 57 yards (rounded down to the nearest yard) from that total. In our 60/40 scenario, it would almost perfectly work out to Spiller gaining 60 yards if we allowed for the unlikelihood of only the two running backs getting rushing stats.
For this purpose, let's assume that Ryan Fitzpatrick gains 11 yards to keep our numbers round. That would have Spiller gaining approximately 54 on the ground this week.
As for touchdowns or an abundance of receiving yards salvaging Spiller's fantasy day? Don't count on it. The 49ers are yet to allow a rushing touchdown to an opposing running back this season, and Spiller's season high in receptions is just three.
Barring for Spiller breaking off a huge run (wholly possible), it seems best for fantasy owners to sit the Bills' star if possible this week. Until both running backs are fully healthy and we know what the split is, there is no way to trust either man—especially against such a top-tier defense.