[A note about pronunciation: if I believe the NBC commentator, Dorjsuren's name is pronounced "dor-CHOOR-in sa-MAI-a". Silva is Brazilian, so the "R" in "Rafaela" is pronounced like an "H".]
Some friends were wondering whether Rafaela Silva's winning throw in the gold medal match might reasonably have been ruled hansoku-make (disqualification), since she seemed to grab the leg of her opponent, Dorjsuren Sumiya from Mongolia.
It's a little hard to tell watching at full speed, but I went through it frame by frame and I'd say it was definitely not hansoku-make. If anything I wonder if it should have been ippon (full point, end of match).
Although it may not be immediately obvious, Silva was countering, not attacking, which I believe is an exception to the rule against leg grabs. I'm pretty sure that alone is enough to settle the matter. Even if that weren't the case, page 23 of this IJF document says that "it is possible to touch the leg of Uke if Tori has both hands in a real Kumi-Kata." The video shows that Silva was indeed gripping with a "real Kumi-Kata" throughout her counter-attack.
Here's my analysis, in four screenshots.
Screenshot 1. It's Dorjsuren (in the white uniform) who initiates the action by going in for hiza-guruma, which begins by planting one foot between the opponent's feet.
Screenshot 2. To continue hiza-guruma, you block the opponent's shin with the flat of your other foot, and you rotate them like a steering wheel, with that foot at the center of the wheel. At least, that's the ideal. The problem is that the opponent's body must already have a little momentum in the direction you are trying to rotate them, or the throw doesn't work, or at least is much more difficult. You can see that although Silva is bent at the waist, her center of gravity is stable and well supported by her legs. Dorjsuren doesn't have the kuzushi she needs.
By doing the steering wheel motion, Dorjsuren has brought Silva's armpit toward her own knee. What happens next is that Silva continues the motion Dorjsuren started and traps Dorjsuren's leg with her right elbow. At the same time, Silva pushes with her left arm. She takes control of the rotation that Dorjsuren started and uses it against her.
Screenshot 3. Silva's counter-throw is well beyond the point of no return. You can see that her right hand has been holding onto Dorjsuren's sleeve for the duration of the throw. Both her hands are in a "real Kumi-Kata". You can also see that Dorjsuren's body is a good foot off the ground, traveling at full speed.
Side note: Dorjsuren has moved her left foot from Silva's shin to her inner thigh, presumably hoping for a counter-counter into sumi-gaeshi. It doesn't work; again, momentum and position are not on Dorjsuren's side, and Silva uses her body weight to squash the attempted counter-counter.
Screenshot 4. You can see Dorjsuren lands about as flat on her back as you can get. That's why I think maybe it should have been an ippon.
Well, okay, Neil Adams said it was waza-ari, but what does he know?