I saw one of Take-sensei's (Steven Seagal) Dan (black belt) grading in a video, and saw the randori. Through observation, Take-sensei saw that it's not only if one could take-down or throw or do any techniques on the ukes (in this case there was like 3 or 4 of them), but it is the spirit of the nage that he is testing.
He made it as real as possible, like he said, the uke can punch, kick, or bite but at the same time the nage is allowed to do the same thing. I saw how the nage is banged up against the wall by the uke, then taken down to the ground and piled up on, while Take-sensei kept saying "ashi, ashi" (legs, legs) - which he means by "the legs are free, use them".
Keeping it as realistic as one wants, but the main important thing of randori, is make it have meaning. If one have a "realistic" randori, but then lost one's center and go into panic or rage, then it has no meaning. On the other hand, if one have let's say a randori that is basically a nagare-type technique applications, but kept the center and extending ki, and feel the opponents ki while practicing it, it will have more meaning.