Player positional defense is something that plays an important part of the game that actually gets the least recognition. If you click on GM's Office, Roster Management, Edit Rosters, your team will be displayed by position. If you click on a players position here it will bring up the editable defensive chart. Please take note of the top of the pop up as it shows the Big League Defensive Averages for each position. Actually I call them the minimums myself if you want good things to happen.
I will use SS as an example. Range is categorized as an 80. I myself won't go below 80 as I prefer above this number. Going down a few points is not all that harmful but will cause a rise in minus plays for the player. I cheat more in glove but wouldn't go no more than 5 points below the advertised 85, going lower causes more booted balls. Dropping down on the arm actually cause more strain on the 1B more than the SS itself as errors abound.
One big thing to note in the defensive realm, only 1B's can throw LEFT HANDED! in the infield. That means 2B, 3B and SS must throw right handed.
In the center of the pop up is the players current/projected ratings so you can compare to the chart. At the bottom is where you can change his position settings the way you desire. The buttons allow for quick settings which most of us use when they are first acquired by the organization. Most generally it is the Show Recs (proj) and then save. Normally it isn't all that concerting until the player gets to the majors. At least you will have a record at the positions that he played and see how good/bad he played at some of them.