Percy Weasley had a sleeper build and knew how to threw a punch. Like you can't change my mind
Since he was 6,3 (according to google) all the muscle in his body gets distributed differently cause if his height. And I would like to think that this would result in a sleeper build. This man had to raise his younger siblings because his poor mother was alway busy and his ather was always working. He definitely got some muscle from doing that and multitasking and picking up his younger siblings because for some reason they always like being held. Then there his older brothers. All that combined, they were clesrly a chaotic little bunch and with older brothers, comes rough houses and practically fighting for your life.
In Hogwarts, he was definitely carrying large stacks of books, YOU NEED STRENGTH TO LIFT THOSE HEAVY ASS BOOKS PEOPLE. At the Burrow, his siblings forced him to play quidditch with him. Let's be for real. He was strong.
Also thinking of all the dangrrous things in Hogwarts. The forbidden forest that was right next to the school, the ghosts, the students (come on, some of them were assholes and bullies.) Percy isn't stupid. He would of taught himself how to fight snd defend and probably knew a few punches. That paired with the fact that he was a little kid in the First Wizarding War, he was probably a bit paranoid and a bit on edge. Therefore he would of convinced himself that he needed to fight because you can't always depend on magic.
Also his roommate, Oliver Wood, was a quidditch fantic. What more can I say? I know damn well he probably dragged Percy to go flying with him and play practise quidditch matches so he could improve his skills for the next quidditch games. That shit requires strength and he definitely built some muscle.
YOU CAN'T DENY IT. THAT MOTHERFUCKER HAD A SLEEPER BUILD AND KNEW HOW TO FIGHT. NO ONE CAN CHANGE MY MIND.