NBA Player Performance Values Part I

This just in! Lebron James, Kobe Bryant and Chris Paul are great NBA players and
I can prove it. My rankings system can look at stats and make that
groundbreaking determination. Of course I want to explain how this miracle works
so I will spend the next few paragraphs explaining our TRU linear weights rating
system.

In the attempt at semi seriousness though I hope that I can offer a little bit
of a different take on the value of basic NBA box score stats and give you
something that gives comparable importance to all stats and not be dominated by
one type of player. Scoring and rebounding both receive their due, but hopefully
in a way that makes some sense to everyone reading this.

I'll go through each typical box score statistic one by one and break down how I
arrived at these values years ago when I used the system to create a basketball
game engine.Not much has changed since except for the fact that similar ranking
systems have become common place. I was originally influenced by Dean Oliver's
Basketball Hoopla in
1988. Long before he wrote what may constitute the bible of basketball stat
based player analysis, Basketball on
Paper. A book that I have still not managed to read. Maybe I should if I
want to be taken seriously. Then again it basketball so I don't need to be. I'm
going to use estimates for the values in the formula. As long as the differences
between a couple of percentage points are not significant enough to alter
dramatically the rankings than we will just keep the number math friendly.
Expect along the way similarites to similar systems. Most of them not
intentional.

The first thing to look at is at what point should we credit players with
creating points when it comes to shooting. I'm not looking for the most
efficient shooting percentages but just a mark where a player is not
automatically hurting his team. A mark where a shot creates an opportunity to
put points on the board. We start with the average value of a possession. The
average value being the average number of points that a complete trip down the
court can be expected to produce. This is consistently very close to one point.
So i'm just gonna use one. (I calculated 1.02 ) If a player creates a two point
shot on a possession as opposed to turning it over than the trip is off to a
pretty good start. By avoiding the turnover either the shot is made or missed.
If the shot is made we credit 2 points for the time being. If the shot is missed
either the defense ends up with it via a defensive rebound or offense keeps
control with a rebound. This NBA season it's about 27% (.27). When this happens
the offense gets a second chance to score so if a player misses a shot it still
has value. For every 100 misses we get 27 second chances. These 27 chances at
one point on average yield 27 points. Since an offensive rebound yields a few
less turnovers and a few more free throw attempts I'll call it 30 points per 100
misses or .3 per missed 2 pointer. The .3 also keeps it simpler and is another
commonly used factor. The shots that missed and are controlled by the defense of
course create no points.

Let me clean that up some with an example. If a player takes 200 2 point shots
than he needs to create 200 points to break even. Anything below that in this
system will penalize the player with negative credits. If he makes 100 and
misses 100 the shooter creates 230 points or 30 points above the "efficiency
threshhold" We can show this as 2 pointers (2gm) * 2 + 2 pointers missed (2gx) *
.3 - 2pointers attempted (2ga) which gives 30 additional points. The break even
point is just under 83 shots or just over 41 percent from 2. Pretty Low. Well
the PER system break even percent is about 30.4%. Wages of Wins (WOW) comes in
at 50. WOW gives all the credit for a missed shot to the rebounders. Of course
ideally a player would make all his shots but only missed shots create offensive
rebounds. 41% is not very good but since a shot missed is better than a turnover
and 41% yields a point per possession than we can live with those misses as long
as you never turn it over and your team can help you out on the offensive glass.
Of course turnovers do happen and they can't be ignored. Of course they are not.
So if you shoot 41% from 2 and you turnover the ball you are going to have a
player with negative credits. Our player with 200 shots if he turns it over at
the average NBA player rate (5.75 shots per turnover) will turn it over 34
times. So now our 200 shot 41% player drops from 200 credits in 200 possessions
to 200 credits in 234 possessions for a point per possession ratio of 85%.
Yuk.That means a player that turns it over a typical amount now needs to shoot,
guess what? 51 percent! Since the more a player shoots the more likeliness in
most cases for turnovers, the small credit gains of shooters just above our 41
percent threshold can easily be lost by additional turnovers. In this way it is
not easy to inflate a players value by merely taking a ton of shots. The only
way to truly be efficient at a low 2 point percentage like 41 is to rarely turn
it over and/or to get to the line often. Only then should coaches encourage high
usage for low percentage shooters. Allen Iverson? Of course three point shots
follow the same principles and we will get to that and more in the next post up.