Earlier this week, I filmed a short clip of a homemade reaction ball. Long time readers of the site may recall seeing the ball before. I first referenced this hand-eye coordination tool back in 2012. At the time, I mentioned how former world champion Kostya Tszyu was often seen training with a similar device (ex. see here). More recently, fighters such as Vasyl Lomachenko have once again popularized the tool. With that in mind, I will use this entry to discuss how you can quickly and inexpensively make a reaction ball for yourself.