I'm not sure if this belongs here or in the MLB section of the message boards, so my apologies is this isn't the place for this.
I've had a love of baseball for quite some time, going from being a casual childhood fan to maybe a moderately less uninformed fan of the game. By that I mean to say that I understand some of the organizational aspects of baseball as well as some of the statistical/sabermetric aspects, but I always feel I lack the understanding of even some casual fans when it comes to the game itself.
Just another little preface, I'm really only going to focus on pitching for these questions, but any hitting and fielding notes would be greatly appreciated.
With that background, what I'm asking is, how do scouts or even fans make certain distinctions based on watching alone? I understand the obvious, like throwing in the mid to high 90s makes for a more effective fastball (though if you can't locate it...eh...), movement on any pitch being another indicator of pitch quality for the most part, and the ability to locate and whatnot, but are command, movement, and velocity (in some regard) really it when it comes to determining whether a pitch is below average to plus? Also, with the insane number of pitchers with different, but effective, mechanics, how is it that a scout determines a "hitch" or something in a guy's mechanics? Does that have to do purely with inconsistency in their delivery? Is it that there are certain ideals for pitching mechanics? Is it just a hunch that a certain change might allow a pitcher to get more on a pitch?
Also, when it comes to pitch selection/sequence/etc, what separates the good from the bad? Is it just a hindsight/don't make stupid mistakes thing? Like supposing a young Kenny Lofton is on first with one out, the pitcher knows he's a base stealing threat, so he starts the next hitter off with a fastball, but the hitter would be expecting that, so is it just a matter of locating it in a spot where the hitter isn't looking for it? Does location then determine whether it was a smart pitch selection in some cases? Or was throwing the fastball a smart choice, leaving it up to location and luck? Would it have been a wiser choice to throw an off speed pitch, and is that subject to being called a poor decision if Lofton steals on the pitch and a good decision if he doesn't? Or does it have to do more with the batter's tendencies than the circumstances? It just seems that so many pitches are only determined to have been mistakes in hindsight. If a pitcher throws a fastball low and away for a strike on a hitter in his first at bat, then starts him off the same way in his second at bat, couldn't that be called predictable if the batter happened to be looking for it but unpredictable if he was not expecting to see the same first pitch and ends up in another 0-1 count?
I apologize if this ended up convoluted and silly, or my lack of baseball understanding is astounding or something, or I'm just completely missing something.