My very-tall-for 10 DS1 refused to hit back. So we took him to self defence classes. Last time someone at school tried to hit him, he grabbed their fist as it was coming towards him, twisted, and the child that was trying to hit him ended up on the floor.
Who got into trouble? Well, it wan't the child that was trying to hit...
Another time, the same child tried to run into DS1 to 'barge' him over. DS1 saw him coming, and adjusted his stance so that he wouldn't be knocked over. The other child fell down on the floor. DS1 was still standing.
Who got told off? For just standing still? Yep, you guessed it. DS1.
I was told that self defence is 'inappropriate' for a school playground where DS1 has been bullied and hurt mercilessly since Reception 6 years ago, and that he should tell an adult WHEN he has been hurt. My answer was that if he is using self defence techniques that are accepted by the police as self defence, then I have no problem with that.
If people don't hit him, he has no reason to use those techniques.
Even at 4yo, when a child was hitting him, rather than hit back, DS1 grabbed the child and held him in a bear hug, as it was the only thing DS1 could think of to stop the child hitting him without actually hitting back.
The child bit him. And drew blood, through a school sweatshirt AND a t-shirt. Guess what the HT said? "well, your DS1 is very tall, it must have been very scary for the other boy to have been held so it wasn't really his fault that he bit..."
Yes, the other boy was so scared of my son that he was hitting him in the first place. 
I have now given up and told my DS1 "Don't hit first, hit hardest."