In what ways do the vR & vL ratings affect a player's abilities?  I have been coming across pitchers with a higher walk rate than you might expect from their control ratings, and typically it seems that their effectiveness ratings are lower (low-to-mid 60s).  Am I imagining a connection where none exists?

It should be mentioned that I have not done much research on this, and right now everything is conjectural based on a few samples that I have run across. 

I tend to think of is as a percentage of how good the rest of their ratings will be against that handedness, be it hitter or pitcher.  It has served me well.

Example:  If a guy has vR in the 30s, it doesn't matter what the rest of his ratings are... he'll get killed by righties.

 

The way I've heard it described (and I think this is a decent way to look at it) is that with hitters, ratings like contacts and power indicate how successful a hitter would be against a pitching machine. So if they saw nothing but straight fastballs down the middle, a 100/100/0/0 hitter could still belt it out of the park every time. But against an actual pitcher, that hitter would be lost. The effectiveness ratings dictate how well the hitter can put those skills to use against an actual pitcher of that type.

The same could be said of pitchers, though it's a bit more abstract in my opinion because of the values of the other ratings; if a guy has 100 control and 100 velocity, he can put the ball anywhere he wants as fast as he wants and usually this alone is the makings of a Hall of Fame pitcher. But in HBD, it's different-- for whatever reason, even having perfect abilities won't allow you to dominate hitters unless you have good effectiveness ratings against them. In this ragard, if you offered me a pitcher with mediocre control and pitch ratings but 100/100 effectiveness ratings, I would much rather take him than a guy with 100 control and great pitches but effectiveness ratings of 35/35. Maybe it's an ability to "fool" hitters, to hide your pitches, to throw them off with your motion... I don't know what effectiveness could be likened to for a pitcher. All I know is it is virtually impossible to be a good pitcher, no matter how good your other ratings are, unless your effectiveness hits, say, 50. And even then, I prefer not to go under 60, and that's with a guy with great control and pitches. 70 is more my comfort zone and 80 is Cy Young caliber with other good ratings. 90's are a special breed if you can get them with good control and pitches.

Excellent explanation, prez!

As with all ratings, they are actaully percentiles (per Admin/CS/DevChat).  50 will be dead on average.... or replacement level, as I prefer to think of it.

My observation is that the vsR and vsL splits for a pitcher impacts the likelihood of giving up hits to RH/LH hitters.  The higher the splits = the lower the OAV. 

The quality (and number) of the P1-P5 pitches modify the splits, so poor to mediocre pitches will bring down the effectiveness of high splits, and good pitches will enhance the effectiveness of mediocre splits.

As iain pointed out, poor splits are going to get killed by major league hitting.  No matter how good the pitches are that modify them.

I've never noticed a direct correlation between walks allowed and lower splits.  Though I can logically speculate that the lower the splits, the more hits (and fewer outs) being produced, thus increasing the opportunities for the pitcher to give up walks.

I've always looked at VL/VR as "command"(the oft-used word of the talking heads), the ability to locate your pitches.   You may be able to throw your fastball thru a tank but, if you lack command of it, you will get smoked because you're hitting the fat part of the plate.    It's different than control, in my mind, because control is the ability to throw strikes.    That enables me to get a mental image of the ratings.   A pitcher with 35 control is wild "out of the zone" and will issue a lot of walks.   A pitcher with 54/72 VL/VR is pretty effective versus RHB but quite pedestrian against LHB.    I think of him as a guy with a knee-buckling curve vs righties that essentially only gets lefties if they give up on the outside pitch.