The following is just my opinion, you can accept or reject any of it as you see fit.
We would all love to have outstanding players at every position, but in most cases our options are going to be limited, and we will have to make some hard choices.
Say youíre inheriting a team with poor overall defense, or drafting a new team from scratch. You want to build a good defense. Where do you start?
I say, focus on two things: defense up the middle and range.
Up the middle defense is crucial. If you have to have a poor defender in your lineup, put him at first, third, left field, or right field. Donít put iffy defenders at short, second, center field, or catcher, unless you have no other choice.
Range is the most important tool at any outfield or infield position (except third base). Range is what turns hits into outs. Itís great to have a player who can throw, itís great to have a player who doesnít make errors, but range will save you the most runs.
Position by position, with each position listed (more or less) in order of importance, and the applicable tools for that position listed in order of importance (tools listed in bold if theyíre really important):
SS: range, arm, turn DP, error
2B: range, turn DP, error, arm
CF: range, arm, error
C: ability, arm
3B: arm, range, error, turn DP
RF: range, arm, error
LF: range, arm, error
1B: range, error, turn DP, arm
All four infield skills are important for a shortstop, but I think range and arm are the most important. A shortstop without range is a third baseman; a shortstop without an arm is a second baseman. Turning the double play is very important for a shortstop tooónot quite as important as it is for a second baseman, but closeóyou might say a shortstop who canít turn the double play should be a third baseman as well. Errors, in my opinion, are of the least concern; a shortstop with tremendous range is going to get charged with errors on a lot of balls that would be scored as singles with a less mobile player at short. Not that I wouldnít prefer a shortstop who doesn't make many errors, but Iíll take the somewhat error-prone guy with great range and a great arm over the sure-handed guy who canít go to his left or right or who doesnít throw particularly well.
I try to never sacrifice defense at short. If I canít get a shortstop who can hit and play outstanding defense, I find one who doesnít hit much but who can play outstanding defense, and then I move on to other concerns. If I have a good hitter who is only average (or worse) defensively at short, I play him somewhere else.
You could argue that the ability to turn a double play is more important than range for a second baseman; you might be right. A player with great range but no ability to turn the double play isn't going to make it as a second baseman, but if I have a choice between two guys who are average at one of those two skills and outstanding at the other, Iíll take the guy with outstanding range and average double play skills. Iíll give up a few double plays for a guy who turns hits into outs. On the other hand, if a guy is below average at turning the double play, I just donít consider him a second baseman at all.
Like a good middle infielder, an outfielder with exceptional range might make errors on some balls that would otherwise be scored as hits. If the batter is going to reach base either way, what do I care if itís scored as a hit or an error? I want a center fielder who turns extra base hits into fly outs; if he makes errors on some of those balls I figure Iím still coming out ahead. As far as arm goes, sure, itís better to have a center fielder with an arm than a center fielder who doesnít throw that well. But if the guy doesnít have range, I donít care how well he throws; Iíll be looking for someone else to play center.
A catcher needs to be able to throw, but cumulatively, his other skills (calling the game, handling pitchers, receiving, framing pitches, etc.) are more important. Exactly how OOTP incorporates this stuff into ďcatcher abilityĒ I donít know, but in this case Iíll give them the benefit of the doubt and assume they do so at least somewhat realistically. Assuming that, ďabilityĒ is more important than ďarmĒ.
A third baseman just needs to be able to throw; everything else is gravy. Range is great, sure-handedness and the ability to turn the double play are nice too; Iíll take all those things if I can get íem. But if a guy doesnít have a good arm, heís not a third baseman.
A right fielder needs to be able to throw too, obviously. Ideally, I prefer to have all three outfield positions staffed by guys with above-average range and above-average arms, but sometimes you have to be willing to put up with a statue out there if itís someone who can carry your offense. I donít like having two slow outfielders, though; if I have two guys in the lineup who are all offense/no defense I prefer to put them in left field and at first base. Iíd rather have a first baseman who can contribute with the glove, but if my poor-fielding first baseman can put up the offensive numbers youíd expect of a middle-of-the-order hitter, I can look the other way.
One of the great things about OOTP is that youíre not stuck having to play someone at ďhisĒ position. In OOTP, as you probably know, players can learn new positions during Spring Training at an accelerated rate; Iím always looking to expand my playersí defensive repertoires during Spring. You can turn a marginal defensive shortstop into a good second baseman or third baseman (assuming he has the requisite skills). You can also turn a player who only plays one position into one who can play multiple positions, assuming he has the tools. I do this a lot. My teams usually have several players who can play more than one position well. When I have a starter go out with an injury, I lose his bat but I usually have someone who can replace his glove.
Also, donít underestimate the value of late-game defensive replacements. Itís one thing to trot a crappy fielder out there everyday because he hits 30 home runs a year; itís quite another to have him playing the field in the bottom of the ninth when youíre up by one run.
How accurately does OOTP simulate defense? I donít know; maybe it does a realistic job, maybe it doesnít. What I do know is that in OOTP the effects of defense can be felt, and building teams that play good defense has served me well.