Playing out of position
You can use a player at a defensive position for which he is not rated, but his performance will suffer. How much? It depends.Players can make a relatively painless transition to an easier position that is similar to one they're already rated for. The penalties are much greater for moving to a very different position that is also more difficult to play.
For example, a CF can play LF or RF without suffering. Both positions are similar and easier than the one he's rated for. A LF or RF moving to CF has a more difficult time because there's more ground to cover. Similarly, a move from SS to 2B won't cost you too much, while a move from 2B to SS will hurt more. And the moves that will hurt the most are (a) from any position to catcher, (b) a catcher moving to any position except 1B, and (c) a 1B moving to CF or another infield position.
How will these penalties show up? In lots of ways. More balls in their zones will go for hits. They'll make more errors. Guys without outfielder throwing or catcher throwing ratings will be easier to run on. Unrated catchers will have more passed balls. Unrated middle infielders won't start as many double plays on balls hit to them, and they won't turn two as often when they're the pivot man on the play.
You might ask why we don't improve ratings when a player is moving to a less difficult position. Couldn't a top-rated SS play 2B even better than the average 2B? In the many years that we've been assigning fielding ratings, we've seen a lot of players get better ratings when they make the transition from a harder position to an easier one (especially SS -> 2B, 3B -> 1B, and CF -> LF), but we've also seen plenty of cases where the player needed some time to learn how to play the new position.
Every position requires of a different set of skills. A CF moving to RF needs to learn how to play the caroms on balls hit down in the corner. A 3B needs great reflexes to handle the hot smashes that come his way, and that might not be the strong suit of a middle infielder moving to 3B. A SS moving to 2B must learn how to make the pivot with his back to the runner.
If our out-of-position adjustments assumed that every player could instantly adapt to a new position, even an easier one, we think it would create too many opportunities for managers to abuse the game by moving players around in ways that real-life managers would never get away with. So the game imposes penalties of varying degrees on all but a very few out-of-position players. The exceptions are (a) center fielders moving to a corner outfield spot, who do not suffer a range penalty or a change in their error rate, and (b) shortstops moving to other infield positions, who don't suffer a range penalty but are given an error-rate penalty.
