I used Brooks Baseball/Baseball Prospectus' heat maps, and for this post, we are only looking at location, and not pitches or anything else. They couldn't be switch hitters because I would have to use extra maps and that would just be annoying. I used the normalized versions for the TAV maps, but not the frequency maps. For a lot of these elite hitters (Ellsbury really isn't an elite hitter, but he is good), they don't have true cold zones, they just have extremely hot zones and zones where they are closer to average.
What I did to test whether or not teams knew their weak spots or not, I looked at their first month's frequency in the big leagues versus their career frequency map and their career TAV (True Average) map. Of course, there are some variables we can't (or didn't) control for using these maps, such as what kind of pitchers they are facing and what may be a small sample size of a first month, but I think this is the best way to approach it.
First, Bryce Harper. Here is his career frequency map, where pitchers have thrown the ball to him in his career:
Here is Harper's TAV map, showing in which zones he has success:
What about Mike Trout? His career frequency map:
Joey Votto's career frequency:
Inside is where Votto goes crazy, but he handles the low and away pitches as well. It can't be fun to pitch to Votto, but here is what pitchers tried to do when he first came up:
Jacoby Ellsbury usually has pitchers trying to go away from him
His TAV map shows that he is a pretty balanced hitter, without weak or strong zones for the most part:
Everything was throw away from him, which I think proves to be erroneous.
Here is how Andrew McCutchen has been pitched in his career:
Middle and low and away is clearly where McCutchen has been pitched. This makes some sense when looking at his TAV map:
McCutchen hits everything in really well, and up and away is his strongest zone. Middle away and low and away is where he is just average. It seems that teams knew this when he came up, as the avoiding throwing the ball up and threw away or low to him
So the reaction seems mixed, but it appears that for the most part, teams some kind of idea where they struggled, with Trout and Ellsbury being exceptions. I wondered if just the general approach was to throw low and away from all of them, and there is certainly a lot of validity to that when you look at the first month map. Just pitching low and away to them seems to be a better description of what teams were doing then finding their weak spots. Traditional wisdom states that rookies usually see more fastballs, though we saw with Bryce Harper last year that he saw very few fastballs. Using FanGraphs leaderboards, we can look at the breakdown of pitch types using MLBAM types for rookies and the league as a whole. First, here are the rookies:
The League as a whole:
The rookies see fastballs slightly more than league average each time (other than 2012 where it is exactly the same), but the results are pretty negligible. League average sees a little more curves, sliders, and changeups than rookies, but again, we are talking about less than a percent most of the time.
My working theory, based on some of this data, is that teams that don't use minor league scouting reports (or what seems less likely, just don't really have them) very much, and that they pitch most rookies about the same as they would other hitters as far as pitch type, with maybe a few less fastballs. However, when big time prospects come up, teams try to keep the ball away from them. It seems that there isn't much evidence that the MLB teams have (or more correctly, use) detailed scouting reports on prospects that tell them which part of the zone they struggle at and which part of the zone they excel.