Many (if not all) of the randori no kata are irimi (entering) techniques. I think I mentioned that in an earlier blog. The key to entering into someone’s space is to ensure that they lose their posture and you keep yours. It is no good moving in close to your attacker if you are bent over accommodating their position and they are all over you.
A classic technique where this happens a lot is gedan ate. Since we need to get low and under the uke’s arms to target the hips for a throw, it is common for people to lean forward and fit their bodies into the shape provided by uke. It is really easy then for uke to lean their body weight forward and down on you to block your technique. It is important that you enter into the position with a straight vertical back, head up. It is most likely you need to get low and below uke’s arms and in line with the hips but this must be done by lowering the knees. The feeling is that as you begin to make contact, with the lower arm and elbow into uke’s stomach area, you are sliding into their position and they are being off balanced. The off balance has to occur throughout from the moment (or before if possible) contact is made. In that way when you get to the point of throwing uke is already going down and the throw is academic; just a matter of turning the hips and maintaining your own posture and balance.
All other irimi techniques require this kind of attention to posture when entering. You can think about aigamae ate, wake gatame and shiho nage in the same way. If at any point during the technique you give back the posture to uke then you have lost the technique. Other techniques such as oshi taoshi and ude garame have a different moment of entering, slightly later after some earlier movement, but the principle still applies. When you are entering you must take control of uke’s space and posture and keep control until they are thrown.