Back to the Basics: The Corner 3
The “Back to the Basics” series is designed to explore the foundation principals of statistical analysis across the four major American sports. The series will provide readers with an understanding of how teams approach roster construction and why certain decisions are made both on and off the field. Readers will also be directed to additional information sources, such as websites, books, or even magazine articles that could substantially increase their knowledge of the subject at hand.
Let’s just get this out the way from the start. The most efficient shot in the NBA is still the two point dunk or layup. Why, because they are converted at a substantially higher rate than any other shot on the floor. In fact, if we break an NBA half-court down into shooting zones, shots taken “At The Rim” [Zone 1] during this season have been converted 55.06% of the time. This conversion rate is roughly 15%-20% higher than any other shooting zone on the floor. Furthermore, getting to the rim substantially increases the odds of a player being fouled and being awarded free throws.
But what happens if you can’t get to the rim for one of those coveted layups or dunks? Well, mathematically speaking, the corner three is the most valuable jump shot available on an NBA court.
Why the corner three? Because: (1) It is converted at roughly the same rate as any mid-range or long two point shot, but is worth 50% more points [3 v. 2]; and (2) The corner three is converted at the highest percentage of all three point shots, making it the most valuable of the three point shots.
Point (1) may be best explained via simple math. For example, given 100 shots from the “Mid-Range Straight-On” area (highest 2pt conversion rate outside “at the rim”), and the same number of shots from the “Corner 3” areas, an average NBA player will produce more points by taking every shot from one of the “Corner 3” zones.
|AREA||CONVERSION RATE||SHOTS MADE||SHOT VALUE||POINTS GENERATED|
In the example above, we can see that even though the player converted an additional two shots from the two point area, the lesser value of the shots allowed the less frequently converted corner threes to generate 35 more points for the team. Taking this example one step further, if I make forty two-point shots and only thirty three-point shots, I will still have generate more points [90 v. 80] on threes than the two-point shots. Therefore, if his conversion rates are similar in each area, an NBA player generates more value by taking a few steps back and attempting a three pointer than he would with a two pointer jumper.
If you’re more of a visual learner, try taking a look at Dr. Kirk Goldsberry’s original submission of “CourtVision: New Visual and Spatial Analytics for the NBA” to the MIT Sloan Sports Analytics conference. Goldberry demonstrated a number of analytical breakthroughs throughout the piece, one of which was his graphical representation depicting corner threes and shots at the rim as the most efficient shot locations on a “points per shot” basis.
Turning to point (2), why is the corner three pointer converted at a more efficient rate than its “above the break” counterparts?* Well, for starters, the “Corner 3” zones [10 and 11] are closer to the basket than the “Wing 3” [12 and 13] and “Straight-On”  zones. An NBA three point line is 22’ from the basket in the corners, and 23’ 9” away above the break, making the corner three an easier shot to convert. Other factors which may help explain the heightened conversion rate of corner threes are:
(1) There is no additional range for a corner three, unlike on the wings or at the top of the key. For example, Steph Curry can pull up from 28-30 feet above the key if he wants to, but if he tried that on a corner three he would be shooting from the second or third row in the stands. The further away a shot is attempted, the less likely it is to go in, so while distance can fluctuate in zones 12-14, it can’t on “Corner 3” looks.
(2) Defensive patterns and offensive schemes lead to more “open looks” from the cornera than at the wings and top of the key zones. For example, one could argue that the baseline inhibits help defense, making it more dangerous to overcommit or overrun a play to the corner as a defender, leading to slower close outs and thus more time to get a shot off.
(3) The guys shooting these corner threes are “specialists” or, to use the popular term “3 and D” guys.
NBA teams are completely aware of this data, which has fostered a shift to offensive schemes with a heavy reliance on the three point shot. One of the most extreme examples of reliance on this type of data is the Houston Rockets, who, as a unit, have shot almost 56% fewer non “At The Rim” two point attempts than the average NBA team this season [1- (408/922)] = .5575
This is not to say that a player should never focus on taking a two point shot. Indeed, there are some players in the NBA, such as Chris Bosh, Luke Ridnour and Kevin Garnett, who convert mid-range two-pointers at such an effective rate that it is more valuable to their teams for them to focus on the long or mid-range two than the three-pointer. However, these players should be considered exceptions to the rule, as very few players convert long two pointers at such an efficient rate.
The “Back to the Basics” series is designed to provide a fundamental understanding of certain principals used in sports analytics, and to demonstrate how they are used in real world decisions. While some basketball purists may detest the current trend of three point shooting in the NBA, one cannot argue that statistical analysis is playing a large role in re-shaping the game. Teams like the Rockets can explain their reliance on the three-pointer, and the corner three in particular, in one sentence:
“If you are going to take a long shot, why not take the one that will give you an extra point?”
Notes: “Above the break” refers to the point where the three point arc begins to curve towards the center of the court.
All data in this article is current up to games played on or after 1/6/14.