It doesn't penalize anything, and it is straightofreward.  It is a simple measure of the percentage of balls in play converted to outs, and as such, it must be interpreted in such way.  DP's are in no way taken into account, nor the other things you mentioned.  This means those must also be considered when veiwing the whole picture, but they are also in no way prejudiced against.

Part 2:

You keep using relievers as evidence, which is already dicey since they have such small sample sizes.  Even from year to year you can't usually expect consistant performance, much less from month to month.  Guerrier improved from April to May because he tripled his strikeout rate, halved his walk rate, and stopped giving up homers (from 2 in 10 innings to 0 in 19 innings).  That's why Guerrier turned it around.  Like I said though, you can't really decide much either way from just those few innings.

Part 3:

It is difficult to say what the bigger culprit was, the pitching or the defense, but both definitly were significant problems.  That is why I'd like t do some dip research with hit in play types to solve issues like this.

Of right, the troll part.

Six that I've seen. I might have mssed a few. But I probably missed some of Castro's as well because you can never tell on the radio, espcially since those guys loved Castro. But I personally saw seven misplays by Castro that I would have scored errors (should have plays), six of which resulted in earned runs for pitchers (six earned runs for Crain in particular). I have not seen one misplay by Bartlett that was not scored an error.

quickness and speed aren't the same. And range includes things like angle to the ball. In fact, I would add this as another of the factors that fans don't really understand.

OK, then I'm going to play the card that I'm no ordinary fan, as you imply of yourself by making the arrogant claim that you are the only one who perceives these things and neither fans' judgements nor statistics can convince you otherwise.

Castro took the worst routes on balls I've seen since Scott Lieus. He would run straight for second on a hard hit ball up the middle and be four steps shy. He hardly ever angled deep in the hole for balls because he knew he could never throw the guy out from the hole. And if the ball was hit right at him, he would go backwards first so that he could circle on it and get his momentum going towards first to get something on the throw. Often these throws would sail up the line and be scored infield hits. As for quickness, he lacked for that as much as speed. He does have quick reactions and quick hands, but not quick feet. And who's to judge positioning. The coaches tell the players where to play based on the book. Castro's nothing special there.

And most of his troubles related to his weak arm. Better to pretend to go after a ball and miss it than to get it and have the guy beat it out by three steps. Better to make the play look spectacular by taking a circular route on a ball than go stratight for it and send a rainbow over to first.

We do? Do they really throw at the same speed consistently? Do we also know who gets rid of the ball more quickly?

These things are measured by scouts, who share them with fans from time to time. But if you can't see the speed of a ball or measure how quickly a guy gets a ball to first, you probably wouldn't believe scouts either. And that's OK. You can go on believing that Castro is better and that is was a big mistake to trade him. For that matter, you can lump this trade in with the one that sent Matt Kinney and Javier Valentine to the Brewers for Matt Yeatman and Henry Bonilla. For, as you have said, more often than not, Ryan's trades have been futile anyway.

Believe what you want, but don't pretend that you have priveledged access to the truth, or that your eyes are better than most fans', or that your way of swizzling the stats is better than others. If you were as skeptical towards your own opinions as you are towards those of others, it would be a lot easier for us to take. But your skepticism becomes sophistry when you fail to apply the same questions to your own opinions.

In this case, you should be quite skeptical of a few percentage points of fielding percentage considering that just one week ago Bartlett had the edge but has committed two errors this past week. Does that make him worse? No. It just means that at this time slice and without any qualifications or margins for error in your measurements, Castro has the slight edge. But the sample is so small that slight changes make a difference. I've seen you use this very argument to support your own views. Yet you fail to use it yourself.