Putting pre-draft measurements into perspective (height & weight)

Here's a link to my first of post of this series - The first step: Height

  The general consensus critique was that people wanted to know where the Bulls players stood in regards to their height.  I put that at the very end and I only plotted data for the six Bulls under contract: Derrick Rose, Kirk Hinrich, Luol Deng, James Johnson, Taj Gibson, Joakim Noah

To recap: last time I presented 5 histograms representing the heights of 200+ players organized by position: 


Unless we're looking to fill out our bench, it probably makes more sense to compare a prospect's height  against the starters in the NBA (below). Not every starter is listed in DraftExpress's measurement database, but here's the height data for all starters that are.


  The scale along the x-axis is the same for all, while the y-axis is different between the two plots. The biggest surprise for me was that the starters at each position are not significantly taller than the league average.  The only data I question is at the shooting guard position, where most combo guards are classified as point guards. So the mean height for shooting guards is probably a bit lower for the general NBA case. For example, Pargo was listed as a point guard, same with Hinrich, even though both played mostly off the ball this year.

  The other point that surprised me was that the difference in height between point guards and shooting guards is about the same as the difference between shooting guards and power forwards. I think understanding the differences that exist between positions is key to differentiating which players are "tweeners" vs which are "versatile." I think it also shows why it's a bad idea to have Hinrich be your team's "best defender," since if he's not guarding point guards, he's in general giving up a lot of height for the position. This has always been known, but I never realized how dramatic the difference was between point guards and shooting guards. 



  I knew that there would be a tremendous amount of variation in the weight data for each position. I thought the variation might be so large that there wouldn't be any discernible trends and that that would make this section even more boring that my first post :). I mean how can Hakim Warrick and Glen Davis play the same position, when there was a 80 pound difference between the two when they entered the league and they are the same height (+/- 0.5 ") . Everything I say should be taken with a grain of salt due to this large variation, but I am convinced that there are some real trends that pop out of this.

To start, I wanted to get a sense of how height and weight are correlated for every player in my database. Here's a scatter of all of the players I have data for:


And more importantly, here's a plot that differentiates between starters, bench, and the Bulls' players.  The hollow circles are bench players, solid circles are starters, and the black squares are the Bulls' players under contract (I'll talk about them last).


This one has a lot of information, which is why I bothered showing the previous plot. It's a good warm-up.


Bench vs starters: Power forwards

  The scatter plot shows that really short stocky power forwards don't start. All of the power forwards that are in the NBA right now around 78-81" and 250+ pounds don't start (they are the blue circle outlines). Those are the the players that are the clear outliers from the general linear spread. The fact that they don't start may reflect that they are not in great shape and can only play for short stints at a time (Some of those hollow circles represent Bass, Blair, Davis, Millsap, & Love).


Compensating for height & weight by position

  If we simplify the data and just look at the general linear trends, an unexpected pattern popped out regarding how we differentiate player positions. I knew that historically short power forwards were not very successful players unless they were really heavy and could power there way around the court. I didn't expect to find a similar trend with short heavy small forwards as well, but it is there to a lesser extent. It seems as if both forward position compensate for their lack of height by an increase in weight. If weight wasn't a factor, you'd expect a positive trend line, certainly not a negative one.


  Here's a plot of the linear trends for weight vs height for each position. I am only showing the data for NBA starters, because it's nearly identical to the data for all players.



  As I stared at these lines wondering what the hell they meant, I had this feeling that it might say something about how we define a player's position. This plot shows you what  two player of similar heights, but different positions, might be expected to weigh, but it tell you nothing about the general distribution of the data. So keep in mind the difference in height between positions as you stare at these lines.

  The proximity of the red and yellow lines in conjunction with the large discrepancy in average height, makes me think that we differentiate point guards from shooting guards by primarily height (average 3.5" difference). It's different for small forwards: the average SF is 2" taller than the average shooting guard, but if he's much shorter, a small forward is differentiated from a shooting guard by weight, but it's clearly rather subtle. Finally power forwards, while only on average 1.5" taller than small forwards, truly differentiate themselves from small forwards by weight, note white space between the green and blue lines.

How important is weight?

  The slopes of the trendlines might be the key to the story. Point and shooting guards have roughly the same steep slope. There's a small offset, but the trend in weight gain per unit height is so similar that it suggests that guards are overall built similarly. The steep positive slope for both guard positions may also tell us about the importance of weight. If weight was a key factor to the guard position, I would expect that the slopes of the lines to be be flatter than they are, or even negative. My rationale is this, height is a beneficial trait and a player has no control over it, but a player does have control over their weight (to some degree). Weight is important for post-play and rebounding, but as a player gets heavy it will usually slow him down. We usually think of guards as being the quickest players on the floor, so it's not surprising that lightness might be more preferable to bulkiness. Bulkiness more importantly also usually influences how one plays, consider the difference in style between Tyrus Thomas & Glen Davis. Forwards can compensate for their lack of height with a different playing style, like becoming more of a power wing (Carmelo, Gomes), or low post bruiser (Blair, Davis).

  While bulkiness and strength can be very beneficial, it's far from a necessity for a guard. There are some guards that can post-up and play well there, most don't. There are some guards that use their extra mass to fight through traffic, but plenty just use their speed + floaters (the comparison of Rose and Tony Parker comes to mind). It might just mean that most guards don't use their size and strength well enough . All things being equal, I'd prefer a heavy strong guard to a skinny one, but the way I interpret the data makes me think that all things aren't equal and that weight shouldn't be too much of a factor when looking at a guard prospect; however, as I tried to point out, for forwards it's a totally different story. 

Finally the easy stuff, the bulls players:

  I didn't label which square represented which players because I think people can figure it outand it's fun to use deductive reasoning. :)

  Taj Gibson and Joakim Noah came into the league as two of the lightest players to currently play in the NBA,and of the current starters in the NBA they easily came in the lightest. IMPORTANT: This doesn't represent their current weight. There current weight can be dramatically different from the weight that they enter. Joakim's has without a doubt added a lot of muscle over the last 3 years. I am showing you their weight when they came into the NBA, not what they weigh now, but everyone is on equal footing, since these are their weights at pre-draft camp.

James Johnson clusters with the small overweight power forwards, maybe we should embrace that. I personally would prefer to see him play more at power forward because he lacks a 3-point shot, and our floor spacing is terrible. When we get an an all-star power forward (every one of which has a terrific jumper), I'll be okay with seeing Johnson play at small forward.


Hopefully, you were able to get something out of this.

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