In Shodokan Aikido, there are four levels of free practice. These are:
Kageri Geiko – Level 1, Uke attacks but gives no resistance to Tori‘s defensive Aikido techniques.
Iki Tatti Gaiko – Level 2, Uke attacks and only resists weak or poorly-executed Aikido techniques by Tori.
Randori – Level 3, Uke attacks fiercely and resists any Aikido technique that Tori attempts. Any throw that works has to be absolutely “spot on”.
These attacks and defenses are done from a soft rubber knife (a tanto), or they can be done from the grasp or punch. Aikido techniques will work against a kick as well, but since the breakfalls are nasty to take when you are thrown from a kick, they are only done this way by the most senior, enthusiastic and athletic of Ukes.
The highest (and optional) level is called Shiai. It is full Aikido Competition, as created by founder Kenji Tomiki Sensei, and I would describe it as Randori done at full-bore.
In Shodokan or Tomiki Aikido competition, Uke takes the soft rubber knife and attacks you for two minutes. Then you both bow (rei) to each other and Uke hands the knife to you.
Now you are the attacker (Uke) and the other guy starts trying to throw you to the ground. Believe me, it is hard work!
It is done on a carefully marked-out area of mat, with not one but two referees watching every move from opposite corners of the square. (So if one referee misses something, the referee on the opposite side will be sure to spot it.)
The only Aikido techniques allowed during these practice sessions of aikido competition are the Randori no Kata (also called the Junanahon No Kata) – the 17 Basic Techniques of Tomiki Aikido. They were chosen for their safety, to protect both players.