When I first saw the story, I immediately thought the same thing. Technically, this ball would be totally illegal.
No foreign materials may be placed in a hole prior to plugging. Additionally, the density of human ashes do not fall in to the density range of plug material specified by the USBC for plug material. Also, the USBC states that "Plugs and designs must be made of material like, although not the same as, the original material out of which the ball was made." Mixing human ashes with plug material creates a material not like what a ball is constructed of, which makes it illegal.
It's a great human interest story and seems like an innocent enough tribute to his father, however from a technical perspective the 300 rolled with the ball cannot be certified if bowled on a sanctioned league. Although, the USBC probably isn't checking as closely as they used to.
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