We added various actuators, sensors, and a micro-controller to a frisbee that could be used to give throw feedback to an ultimate frisbee player.

Here's an excerpt from the paper:

Ultimate frisbee is a rapidly growing sport that is played in more than 42 countries. Although it is often seen as a lighthearted pastime, significant training and practice are necessary to achieve an average level of throwing proficiency, and it is difficult for new players to map the flight of the frisbee to their throwing action. In this paper, we present Ultimate Trainer, a frisbee augmented with electronics that gives a player visual and haptic cues based on grip strength and angle of release, along with flight information such as rotation speed and time of flight. We give a brief account of our design and implementation with results of preliminary testing.
Augmenting a frisbee with electronics presented a few obvious design challenges, the most significant of which involved minimizing the additional weight and aerodynamic footprint of our system. We targeted the augmented frisbee to have no more than a 10% weight increase from a standard 175g ultimate frisbee.

Short video of this system in action:

Software: Micro-controller code written in C, throw data visualized using D3.js
Hardware: Arduino Nano, MPU-6050, a triple axis accelerometer and gyroscope, a microSD card breakout board, 3.3V Li-Ion battery, a custom designed and etched PCB, and an ultra-light 3D printed case

Related Publication(s)

Cynthia Solomon, Amartya Banerjee, and Michael S. Horn. 2014. Ultimate trainer: instructional feedback for ultimate frisbee players. (TEI'14)