This is what the announcers tell me:
Good receivers make plays in space. They are a flighty bunch.
A good running back runs north and south. They are more grounded than receivers (see Chad Ochocinco).
A bad running back runs east and west. Are all the fields oriented the same direction?
A good running back runs vertically. That's north, right?
A good quarterback can see the field. He also has "touch". Taste and smell are not critical senses for a quarterback. Though I imagine that Tom Brady has taste and Rothlisberger smells.
A good quarterback has an arm. One is apparently enough.
Legs are good to have, though more than one is required to make plays with, unless you are a kicker.
Some quarterbacks used to be "mobile".
Now these quarterbacks are "athletic". That means they can run. With their legs.
Having legs to make plays with seems to have replaced footspeed as a positive attribute.
An arm is good, legs are good, a foot is good. Joints are not good to have. If a player has "a knee" or "an ankle" or "a shoulder", he is either out with it or bothered by it. Neither one is good for his game.
The same goes for Jessica Simpson.