The quarter mark of the NFL season is a good check-point for fantasy owners. It’s a time to analyze your roster and cut bait with players who are dragging you down. Waiting until the mid-point of the season may cost you a playoff spot, so for those hanging around the middle of the pack or worse, it’s time to get aggressive and upgrade your roster.

BUY: Ryan Mathews

Although he insisted he wasn’t trying to send Mathews a message by giving him fewer carries than Jackie Battle in Week 4, Norv Turner’s actions spoke crystal clear. Mathews has been plagued by fumble problems throughout his entire career (11 fumbles in 27 career NFL games), and a costly Week 3 fumble in the red zone against the Falcons did not sit well with the coaching staff. Hopefully, two weeks of a lighter-than-usual workload for Mathews has led the owner in your league to become dissatisfied with him.

Turner made the ruse of taking blame for the Week 3 fumble, saying he gave Mathews too much work for his first game back after recovering from a broken clavicle. So a reduced workload in Week 4 shouldn’t have been a surprise. Turner was also so effusive in his praise of Mathews after Week 4 that it was clear the current timeshare will be short-lived. According to beat writer Kevin Acee, “Turner could not stop praising Mathews” after Sunday’s win over Kansas City.

The worst case scenario for Mathews’ owners is that Jackie Battle will take away some of his red zone touches. This would be a familiar situation, as Mike Tolbert vultured all his red-zone opportunities last year. Mathews still finished 2011 as the 10th-ranked back in standard fantasy leagues, showing that Tolbert’s presence had little impact on his value. If he can hold onto the rock and his red-zone touches, he’ll likely become a top-5 RB for the remainder of the season. Now is absolutely the time to pick him up at a discounted price.

Players I would trade away to get Ryan Mathews: Alfred Morris, Stevan Ridley, BenJarvus Green-Ellis, Darren McFadden

SELL: DeMarco Murray

What used to be considered the strength of the Dallas Cowboys is now their biggest weakness – the offensive line. This rag-tag group of lineman has led to the downfall of DeMarco Murray thus far in 2012. After a strong start against the Giants’ mediocre rush defense, Murray hasn’t topped 45 yards in any of his other three games. His 41.1 standard fantasy points this season rank 20th among running backs, and his 3.9 YPC rank 26th. Murray is a strong runner and has all the tools to succeed, but he’s running into brick walls week after week behind this porous o-line. Over just the last two weeks he’s had 14 rushing plays for negative yards, after having just 13 during his entire rookie season (164 carries).

The bad news for Murray and his owners is that there appears to be no end in sight. There are no injuries on the offensive line, and apart from the snail-paced improvement of second-year left tackle Tyron Smith, this unit will not be getting any better as the season progresses. Future matchups with Baltimore, Philadelphia twice, and a stout Browns defense won’t help his cause. The conclusion to be drawn here is that we should view Murray as a sinking ship and abandon as soon as possible.

Players I would target when trading away DeMarco Murray: Willis McGahee, Trent Richardson, Michael Turner, Doug Martin

BUY: Stevie Johnson

At the beginning of the season there was debate as to whether or not Johnson is a viable WR1 or just an above average WR2. His 37.5 fantasy points through four games — which rank 22nd among receivers — are an indication that he belongs in the latter group. However, there’s reason to believe we have yet to see the best of Stevie this season.

Johnson has the lowest catch percentage of any of those top 22 receivers (just 41.7 percent). This is not a result of frequent drops, as he only has two on the season. It appears to simply be a slow start for Johnson and his quarterback Ryan Fitzpatrick. There’s no reason to believe Johnson’s catch percentage shouldn’t return to the mean as the season progresses, as last year it finished at 56.7.

A torn ACL in David Nelson’s knee has left the Bills very thin at receiver, and it should lead to more looks for Johnson. Buffalo’s defense has also not lived up to expectations, leading to Fitzpatrick and the Bills being forced to air it out earlier than they might want to, which is also good news for Johnson owners.

The final point that leads me to believe Johnson is more valuable than he appears is his red zone opportunities. He currently ranks third in the NFL with five red zone targets, which bodes very well for his future production.

Players I would trade away to get Stevie Johnson: Dez Bryant, Brian Hartline, Lance Moore, Danny Amendola