Why is Johnny so special? Why does he have to be protected by the other greasers?

Johnny was the gang's pet," everyone's kid brother."But after being beaten badly by the Socs four months before the action of the story commences, he is "jumpier than ever." He was always "high-strung," living in a household where his parents beat him all the time. When the Socs attack him and Ponyboy, he kills Bob to stop them from drowning Ponyboy. Dally especially tried to look after Johnny because he understood Johnny's bad home life.