Saturday, May 6, 2017

Free Throw Deep Dives: The Windup and the Release

Part three of an infrequent series. Click here to go straight to the interactive tool.

In previous free throw deep dives, I used SportVU ball tracking data to examine how launch angle and release spot affect free throw accuracy. In this post, we back things up a bit, one second to be precise, and dive into the specific mechanics of each player's free throw shot.

For this free throw analysis I focused on the motion of the ball (in all three dimensions) for the second prior to the ball being released. One second, while somewhat arbitrary, was chosen so that I'm capturing the natural shooting motion of the player after any pre-shot routine has been completed (e.g. one dribble, two dribbles, Klay Thompson's weird arm tap thing, etc.).

The ball tracking data is messy, and shooting motion will vary from shot to shot, so I built a simple LOESS model for each player, with the goal of teasing out a player's typical shooting motion in all three dimensions. LOESS models are nice because they don't force you to shoehorn your data into a pre-determined type of curve (e.g. polynomial, exponential, etc.).

Here are the results for Kevin Durant's typical shooting form:

Imagine you have courtside seats right around the free throw line and the hoop is to your left. The blue line above charts the path the ball will follow from your vantage point for the second prior to the release of the ball. The gray line is a benchmark of sorts. It is the path one would expect for an average player of Durant's height.

From the chart above, we can see that Durant's windup is much longer than average, which is not too surprising, given his above average wingspan.

Now imagine you're hanging from the rafters of the arena, looking straight down on the court. Here is the path the ball traces from that perspective:

Right handed shooters tend to release the ball somewhat left of center from the hoop. More generally, players like to shoot free throws away from their body, rather than across it. For example, here is the overhead view for left handed shooter James Harden:

Year to Year

My dataset goes back to the 2013-14 season and stops about halfway through the 2015-16 season (January 23, 2016 to be precise). In addition to running all available shots through a single analysis, I also ran one for each player and season separately. My goals were twofold:
1. To see if I could identify substantial shifts in a player's free throw mechanics from one season to the next
2. Perhaps more importantly, it was a good validation of my methodology. If the "windup" curves for most players looked similar year to year, it means I am measuring something real and not being fooled by noise.
With a smaller sample size, the results get a bit noisier at the season level, but consistent patterns emerge for players with significant shot volume. For example, LeConsistency:
You can find these results for each player by clicking on the "byYear" tab of the interactive tool.

An excursion to Waiters Island

In a recent article for Nylon Calculus, fellow minutiae enthusiast Matt Femrite noted a peculiar pattern in Dion Waiter's free throws. He misses an abnormal amount of his second free throws after he makes his first, and he makes an abnormal amount of his second free throws when he misses his first.

My year by year results revealed another peculiarity of Waiters' free throws:

Dion is a right handed shooter, and for the 2013-14 and 2014-15 seasons, released the ball from left of center, as nearly all righties do. But in 2015-16, his releases point shifts dramatically to the right. It turns out this was by design:
Wanting to stop the continual decline of his free-throw percentage, Waiters watched film of his technique in the offseason and noticed that most of his misses would go to the left. Believing that this was because of where he positioned his feet on the free-throw line, Waiters has decided to shoot his free-throws this season by standing as close to the right elbow as possible.

Comparing Two Players

On the "compare" tab of the interactive tool, you can also lay alongside eachother the windups of any two players in the dataset. We can use this tool to test the effects of nature vs. nurture on free throw mechanics:

And my favorite, Marc Gasol vs. Pau Gasol:

The Lists

The final tab of the tool, labeled "top20", ranks players by metrics derived from my free throw analysis:
• Most / Least Idiosyncratic
• This ranks players by how much their actual windup differs from the typical windup for a player their height. It turns out that, by this measure at least, Robin Lopez has the weirdest free throw shot in the league.
• We also now have mathematical quantification of how ugly and peculiar Joakim Noah's free throws are.
• The table below shows the most conformist free throw shooters, but that's not nearly as interesting.
• Longest/Shortest Windup
• This ranks players by how much distance the ball covers in the second prior to release. Once again, Robin Lopez tops the list here. His free throw windup covers 7.08 feet in one second (Kevin Durant comes in second at 6.77 feet).
• When it comes to shortest windups, Mike Conley is an extreme outlier at 2.60 feet
• Blake Griffin, with his odd free throw release mechanics, comes in second with a windup of 3.36 feet.
• Biggest / Smallest Change Year to Year
• Creating this list is how I (re)discovered Dion Waiters' shift to the right.
• Michael Kidd-Gilchrist is known for his peculiar shooting mechanics, and his struggles in correcting his form have been the subject of multiple articles. You can see those year to year struggles displayed in chart form here.
Suggestions on additional ways to view/analyze/slice this data are welcome either here in the comments or on Twitter.