Because of his athletic ability, popularity, and looks, Darry would have been accepted by the Socs had he not chosen to recognize his family roots and associate with his friends and brothers. Darry made the decision that his extended family (including the other boys) was more important than belonging to the "in crowd". He threw away an athletic scholarship, which would have given him recognition and social standing via performance and education, in order to take care of his family. Darry's priorities kept him from being a Soc.
When, in Chapter 8 of S. E. Hinton's novel The Outsiders, Two-Bit Mathews tells Ponyboy, "You know, the only thing that keeps Darry from bein' a Soc is us," he is referring to Ponyboy's oldest brother Darryl being more mature, more disciplined, and more responsible than the rest of the Greasers. Ponyboy's response to Two-Bit's observation serves to reaffirm that his oldest brother should have had more opportunities to shape and direct his life but was locked into the Greaser existence by virtue of the responsibilities thrust upon him by the premature deaths of their parents. Ponyboy follows Two-Bit's observation with the following thought that reinforces Two-Bit's comment:
"I know" I said. I had known it for a long time. In spite of not having much money, the only reason Darry couldn't be a Soc was us. The gang. Me and Soda. Darry was too smart to be a greaser. I don't know how I knew, I just did. And I was kind of sorry.
Back in Chapter 1 of The Outsiders, Ponyboy introduces the reader to his brothers, Darryl and Sodapop, the latter a more congenial, easy-going and sensitive partner. Darryl, in contrast, is serious and domineering, forced, as noted above, to assume the role of parent to his younger brothers. While Sodapop holds down a full-time job as an auto mechanic, he is relaxed and upbeat when home. Darryl, in contrast, "works too long and hard," and treats the youngest brother "as if I was six instead of fourteen." Two-Bit's observation regarding Darryl emphasizes the latter's tenuous connection to the rest of the Greasers. He is a Greaser, and is loyal to his neighborhood and friends. Unlike most in this neighborhood, and unlike with most of his friends, Darryl could attain something better in life. Circumstances, however, preclude any such opportunity.