What if the person is bigger and stronger than me?

Assume they are. Nobody picks a fight they expect to lose, so if it is coming to you, it is coming from somebody who likes their odds.

Now the honest part. Size and strength matter. Anybody who tells you otherwise is selling a class. A hundred pounds is a hundred pounds and no trick makes it disappear.

And yet Brazilian jiu-jitsu exists because of this exact question, and the answer it found is leverage. You do not meet strength with strength. You change the angle so their strength has nowhere to go. A grip is weakest at the thumb. A body is weakest sideways. Somebody driving forward hard is somebody who cannot stop, and their weight becomes a problem they have to solve rather than one you have to absorb.

So what I coach a smaller person is short. Do not trade punches with reach and weight. Move off the line instead of backwards. Break the grip with hips and legs rather than arm against arm. Get to your feet and get to the door. The goal is the door, not the win.

This is the same question people ask in grappling, and the answer has the same shape. Strong beginners beat weak beginners. Once technique is in the picture, strength stops being the deciding vote. Do you need to be strong for jiu-jitsu goes through it properly. Conditioning still helps, because a gap closes a little with work and a lot with skill: do I need to be fit.

If you are a woman and this is why you are reading, start with the specific situations rather than the general principle. Grips, distance, getting off the floor, getting to the car. What a woman should learn first is that list, in order.

None of this is legal advice about using force. Talk to a lawyer about that.