The argument was that he initially made contact with the heel of the stick, which was just below the crossbar. Supposedly, RDS had an angle that we never saw on Comcast that backs this up, though it's not iron-clad.
The Richards penalty was BS, though. There is a YouTube already, and it's clear that the initial contact was made with his shoulder into Kovalev's side, just above his hip in the lower rib/kidney area. It shouldn't have been called. At first glance, though, it looked like a trip from the speed and the leg whip from Kovalev.