Nylon Calculus 101: Basic Shooting Statistics
By Ian Levy
One of our missions here at Nylon Calculus is to help make basketball analytics accessible to anyone with interest. A big part of that mission is building a comprehensive and reliable Glossary. The plan is to make this glossary different from some of the others around the internet in two ways. The first is that it will be top-to-bottom comprehensive and sequential. The thing that is often lost in discussions about basketball analytics is that each new statistic or technique is usually an adjustment to a previous model, trying to account for some hole or something that isn’t measured well in existing statistics. All basketball statistics have a lineage of mathematical models and we want to make sure that anyone with the time and interest can peruse the entire family tree. The second thing that I believe will set our glossary apart is that we want to do more than define the statistics. For each we would also like to explain a little about what it says and what it doesn’t say — what purpose it serves in our analytic discussion.
We’re just getting started with our Glossary and there’s a lot more to build. We’ve already looked at The Basic Box Score and this entry will delve into basic shooting statistics. From here we can begin to start looking at how the basics are adjusted to create a more complete picture of what is happening on a basketball court.
Basic Shooting Statistics
Field Goals and Field Goal Percentage
Field goals are any shot from the field, encompassing both two and three-pointers. Field goal percentage is the most basic measure of shooting efficiency, simply dividing a team’s or player’s made shots by their attempted shots. Field goal percentage is then an average of how often the ball goes in the basket when it is shot by a team or player. In 2013-2014, the average field goal percentage across the entire league was 45.4%. Although it depends greatly on context, in general a field goal percentage below 45.0% is considered less than ideal. A field goal percentage above 50.0% is considered very strong.
However, being one of the most basic measures, there are several problems with using field goal percentage as a measure of shooting efficiency. The first is that the term field goal covers every shot and as such field goal percentage can be measuring vastly different things for different players. For example, both Kyle Korver and Joakim Noah had a field goal percentage of 47.5% last season. Korver is a perimeter marksman, while Noah shot attempts generally come much closer to the basket. While both made shots at the exact same rate the fact that they did so in different roles, from different locations on the floor and providing different values (when you factor in how many of Korver’s shot attempts were three-pointers instead of two-pointers). This means it’s messy to draw a direct comparison between the two of them in terms of shooting efficiency, even though they had identical field goal percentages.
In the end, field goal percentage is a good place to start an examination of a player or team’s shooting efficiency, but often additional information and context is necessary.
Three-Pointers and Three-Point Percentage
Three-pointers are any shot taken behind the three-point line and, as the name implies, this subset of field goals provides three points for a made basket instead of two. Like field goal percentage, three-point percentage is just a ratio of made three-pointers to attempted three-pointers, and shows on average how often the shot is made when a player or team takes a three-pointer. In 2013-2014, the average three-point percentage across the entire league was 36.0%. Generally below 35% or so is considered unreliable three-point accuracy, above 40% is considered elite.
Looking at three-point percentage helps add some context to a comparison done with just field goal percentage. But things can get misleading because the scale of what’s considered good shooting from the field and specifically from behind the three-point line don’t necessarily line up. When looking at three-point percentage it’s also important to consider things like the rate of attempts, essentially the sample size for the shooting percentage.
Free Throws and Free Throw Percentage
Free throws are shot from the free throw line and earn a single point for each make. They are not a subset of field goal attempts and, as such, represent a different realm of shooting efficiency. Free throw percentage is the ratio of made free throws to attempted free throws and shows, on average, how often a free throw shot is made when taken by a player or team. In 2013-2014, the average free throw percentage across the entire league was 75.6% and the league average has hovered around that mark for essentially all of the modern era of NBA basketball. Anything below 70% is considered poor free throw shooting. Generally, a free throw percentage above 80% is considered very strong.
Being a separate class of scoring from shots taken during the flow of the game, free throw percentage is often considered an addendum to a player’s shooting efficiency. Like with three-pointers, considering the rate of attempts is very important when evaluating free throw shooting.