Was the kick illegal? Here's a translation of the Yarennoka rules from Fightlinker. They were able to get Roxy Modafferi to translate.
So…I read the Japanese rules, and it says: When someone is in the four-point position (with both hands and feet touching the ground) soccer ball kicks to the head and face are illegal, but knees aren’t. Then it said something like “BUT in the case of Fedor and (the other guy) it was a foul. (huh?) Then it said “that’s just a hypothetical situation.” (huh?)
Nightmare of Battle MMA Blog also had a post regarding the rules here. Basically, soccer kicks were illegal. The problem is that Akiyama is borderline lifting his hands off the ground. All fours on the ground counts as a downed opponent according to the rules.
Watch the video below to determine for yourself.