Always protect yourself (circle of protection) and take the bully down.
If he takes you down, you need to escape the pins to recover your guard (snake). Use your guard to protect yourself and get on top (sweep).
Once on top, you need to pass his legs and establish solid control. In this position, you can negotiate and find a way to resolve the issue with the bully.
MINDSET: Bullies don't attack anyone and everyone. They are predators who very carefully pick out the persons they think will make the easiest prey. They don't want someone who will fight back.
Walk with confidence, knowing that you can deal with the situation if it gets out of control. Never look for a fight, but stand up for yourself when you must.
Once on the ground, you are the shark, and they can't even swim!
