Re: Regrading grabs in Aikido...
Many attacks from behind were to prevent drawing out a sword, or/and to choke in the same time. Attacker didnt simply grab and stand waiting gently until you will have a good mood to do a technique. Attack from behind was/is to pull you down to the ground and to hurt/kill you.
Also, these kind of attacks are very difficult to deal with. One must develop 6th sens to feel attack just before someone touch you, without looking back.
It is very important part of practice.