ALLEN PARK - OK, it's kind of a trick headline because Detroit Lions receiver Derrick Williams is not changing positions. To make the Lions' final 53-man roster, though, Williams may have to beat out a running back.

It's always a numbers game when the final cuts come and the Lions are set with their three quarterbacks and three tight ends and they're not going to cut back on the offensive line. That leaves basically one "flex'' position. What is more valuable to head coach Jim Schwartz - that fifth running back spot or that sixth receiver position?

It would appear that if Williams, a third-round pick three years ago, will have to make a convincing case. It's likely that Detroit's top five receivers are set - Calvin Johnson, Nate Burleson, Titus Young, Rashied Davis and Stefan Logan. Davis and Young are superior special teams players so there's almost no chance Williams can unseat one of them (particularly Logan).

At running back, there are some questions about that No. 5 running back spot. Jahvid Best and Mikel Leshoure are on the team and Detroit should keep its only true fullback in Jerome Felton. That leaves two spots and one of those (if not both) could be filled by Maurice Morris or Aaron Brown. It's more likely Schwartz will choose between those two and we're down to one final position.

Here's where it gets a little tricky for Williams. While he's had a very strong camp in catching the ball and proving himself as a receiver, he needs more value so he has to step it up in all special teams. Even that, though, might not be enough. The reason is because that No. 5 running back will likely be able to do three things instead of just two. Guys like Joe Jon Finley or Richard Dickson or Preston Dial can play fullback, tight end and also contribute on special teams. Offensive coordinator Scott Linehan likes having that extra punch in the backfield where he can move that tight end/fullback around for better matchups.

We hear Schwartz talk about positional flexibility all the time and Williams has to take that to heart. Williams has four preseason games to show that he can be an outside receiver, a slot receiver and a special teams demon. This will be interesting to watch.