Was I wrong in this parenting situation?

My son told me that there’s a boy in his 4th grade class that punches him in the stomach and really hard on the arm the last few days at school.
He said this boy hit’s everyone in the class.
He said he tells the teacher and they tell the boy to stop and send him to the office, but the boy doesn’t care and just hits my son again as soon as he gets back.
I told my son that I could talk to the Principal, but he said not to yet.
He said he’d keep telling on the boy if he does it more.
I asked my son if he ever defends himself from that boy and he said that boy is a big cry baby and if anyone does anything back he cries and tells and my son would get in trouble.
My son is a good kid and he told me he wouldn’t hit back even if that boy keeps punching him.
My son grabbed his stomach and told me it still hurts.
I asked him if the boy is bigger, he said no and I told my son that I could talk to the Principal or maybe you could surprise that kid with a little punch in the stomach when nobody’s looking because he sound’s like he need’s to know how it feels.
My son said he’d never do that.
I don’t know what to tell him because I don’t want him to hit anyone, but sometimes the teachers can’t stop a bully and it gets to the point where you have to try to defend yourself.
Anyway, I will always go through the proper channels and contact the Principal if it continues, but was I wrong to tell my son to consider hitting that boy back or at least stomping on his toes and whispering to him “Don’t touch me again?”