In these kind of situations there is no how to manual. instead, don't reley on one certain defense predetermined, but just let your training take over.
Fopr instance I was attack once wile sitting, these guys heard I was in MA and they wanted to test me. Well, They didn't want me kicking them, so in there half witted attack they stood on my feet, thinking it would make me immobile. Well an array of punches came at the rest of my body, me blocking and countering most of them., I'd say they each got one good one in on me. All wile I am sitting down in a chair. I decided that if I where to win I have to stand up, so what I did was that i slouched down in the chair almost on my back, cslip out from under there feet and pushed them both away at the same time with somewhat of a double stomp kick. Then standing up to finish them off.
Now if you ask me to do all of that again in the dojo, it probably will not be anywhere near the way it was that day. The adrenaline was pumping and I felt that my life could be in danger. So I reacted.
None of this was predetermined on how I would fight sitting down, but its just like grappling....All the tech. you do standing up, you can do just as effectively and the ground, with a few slight modifications.
Regards