Week 15 Fantasy Rankings: Rashard Mendenhall and Stars You Just Can't Trust

The fantasy football playoffs are in full swing, so all the marbles are on the line. If you've made it this far, you must have a pretty good team. Normally, the best advice is to trust the guys that got you there. However, since every lineup decision is life or death (in fantasy terms, of course), you can't afford to make a bad one.

That doesn't mean that you should definitively sit your star players if they have undesirable matchups, but if you have good alternatives, then it's something to think about. Here are three fantasy stars that you cannot count on for big production in Week 15.

Kevin Smith, Detroit Lions

I understand that Detroit Lions running back Kevin Smith may not be considered a star by most. However, when he has been on the field this season, he has most definitely played like one. Smith has been filling in for the injured Jahvid Best over the past month, but he has had some injury problems himself in the form of an ankle ailment.

Smith left the team's Thanksgiving game against the Green Bay Packers early due to the injury and did the same the following week. He missed last week's game against the Minnesota Vikings, but seems in line to play against the Oakland Raiders on Sunday.

Smith has put up great splits that likely would have led to monster games in the contests he left, but he can't be trusted.

If Smith were 100 percent healthy, I would certainly advocate playing him against Oakland's 29th-ranked run defense. The problem is, if Smith comes up lame again this week, it could very well cost you your season.

If you have absolutely no other option, Smith is a good boom-or-bust play, but don't risk it if you don't have to. 

Cam Newton, Carolina Panthers

Carolina Panthers rookie quarterback Cam Newton was either a late pick or went undrafted in most fantasy leagues this season, but he has far outperformed anyone's wildest expectations. Not only has he been successful as a passer (with 3,573 yards and 15 touchdowns), but he is a major threat as a runner as well (with 554 yards and an incredible 13 scores).

Newton has been a revelation this year, but he has about as bad of a matchup as you can ask for against the Houston Texans this week. The Texans quietly rank in the Top Five in the league against both the pass and the run, which makes this game a very tough one for Newton. Owners have a tough decision to make.

If you have Newton, there is still a decent chance that you have another good quarterback because Newton was a late pick. If that is the case, you might want to make a switch. If that isn't true, however, then you may have to bite the bullet.

Newton may be able to scrape together enough for an acceptable week, but I don't see him going off and there is certainly a threat of turnovers as he has already thrown 16 picks this year. 

Rashard Mendenhall, Pittsburgh Steelers

Pittsburgh Steelers running back Rashard Mendenhall was a late-first or early-second-round pick in most fantasy leagues this season, but he hasn't really lived up to expectations. While he has scored eight times, he has rushed for just 710 yards with three games remaining. Some of that is due to injury, but there has also been a change in philosophy.

The Steelers are no longer the smash-mouth team we have grown accustomed to on offense. The Steelers have been far more successful whilst spreading the field and allowing quarterback Ben Roethlisberger to pick apart opposing defenses. This, in turn, has really cut into Mendenhall's production.

When you take all of that into account, and consider that he is playing against the San Francisco 49ers this week, he is a prime candidate to bench. The Niners are the best in the league against the run. They give up barely more than 70 yards per game and have yet to allow a rushing touchdown. There simply isn't much scoring potential for Mendenhall on Monday night.