I haven't gotten all the way through it, but I did notice:
Quote:
"The ball therefore rotates about two different axes simultaneously."

Which would appear to violate
Euler's rotation theorem which states that "any displacement of a rigid body such that a point on the rigid body remains fixed, is equivalent to a single rotation about some axis that runs through the fixed point.".
One could argue that the point is semantic, but I wouldn't expect such a fundamental mistake in a peer reviewed article.
Thank you kindly.