Re: Defending against Aikido
respectfully, the question is unanswerable since there are way too many variables that are assumed or are assumed away. Size, strength, location, distance, speed....just to name a few.
If he has you off balance AND knows what he is doing, AND assuming it was an ambush attack, which if you were for arguments sake being attacked by a skilled martial artist, then he skillfully has employed the art of suprise and has a huge advantage over you. He is probably already two or three moves ahead of your recovery and is moving you into position for the next submission or strike.
You are probably screwed if he knows what he is doing. Do what you can to recover yourself. I recommend going to the ground and into the guard to be quite honest since you are probably headed there anyway. All the more reason work on ground fighting skills.
BTW, people don't attack with a pure martial style like using "aikido". They may use principles, but in the end they use what works based on all the variables and errors that present themselves in the situation. Ends up looking like NHB or MMA stuff when being done for real. That is why I say go to the guard...it is the most likely position of defense you will be able to acheive.