I didn't understand what was illegal in the Keller - Peterson match. To me it looked like Peterson tried to reverse Keller by rolling him. Then while Peterson was sitting on the mat partway through the roll, Keller did a figure 4 on Peterson's head and arm and tried to put Peterson on his back.

I don't know the rules, so if someone could explain I'd appreciate it. An earlier comment stated you couldn't do a figure 4 on a head unless you were in a pinning combination and it sure appeared that Keller was trying to pin Peterson with that. Also Peterson's arm was inside the figure 4 (Keller's leg went under armpit and across chest). Without knowing the rules I would guess it to be like head and arm; With arm - okay, headlock without arm - illegal

Can anyone explain the applicable rule?