@Martinobortino,
Not necessarily a good reason for picking up a
fighting sport.
However, if you are really interested in martial arts for less questionable reasons...Muay Thai
You can be an expert Muay Thai fighter and get clocked by a big ox twice your size, but it can keep a larger opponent away from you (kicks) and perhaps finish them in a clinch.
Kicks are the great equalizer.
My father taught me boxing (He was a boxing champion in the Army), and it served me very well, but it was only so good against a big ox who didn't mind me repeatedly hitting him in the nose.
When boxing against a larger opponent you have to be very fast, and you have to hope that the lug doesn't like a nose bleed. Most don't, but every now and again you find yourself in a fight with the wrong guy, and then you need to be willing to absorb punishment. Fortunately for me, I never got in a fight with someone who could have killed me who was not willing to kill me. Most of those such fights involve weapons.