Hinton foreshadows the fights between the greasers and the Socs and the trouble that Johnny and Pony will get into.
Foreshadowing is the author’s use of hints at future events earlier in the story. One example of foreshadowing is when Pony describes the trouble that greasers get into with Socs.
Greasers can't walk alone too much or they'll get jumped, or someone will come by and scream "Greaser!" at them, which doesn't make you feel too hot, if you know what I mean. We get jumped by the Socs. (Ch. 1)
In fact, Pony and Johnny are going to have a lot of trouble with the Socs throughout the book. The Socs jump Johnny, and beat him badly. Pony is also targeted by a group of Socs, but the others in his gang are able to intervene before he is too badly injured.
When Johnny is jumped, it also foreshadows the incident in the park when Johnny and Ponyboy are targeted again. This is the more serious incident, because in fact Bob is killed when Johnny is trying to defend Pony from him.
We backed against the fountain and the Socs surrounded us. They smelled so heavily of whiskey and English Leather that I almost choked. I wished desperately that Darry and Soda would come along hunting for me. (Ch. 4)
Each time Johnny is attacked, it is serious. The second time, he defends himself because he has to. He and Pony head to the church on the run, and it is there that they defend the children from the fire.
Johnny is badly injured in the fire. The greasers are very angry about the incident in the park, and they decide to get payback against the Socs. But before the rumble, Pony has a conversation with one of the Socs, Randy, who tells him that he no longer wants to fight. It foreshadows Pony getting out of the life. He sees Randy as just a guy, and tells Two-Bit so.
I still had a headache, but I felt better. Socs were just guys after all. Things were rough all over, but it was better that way. That way you could tell the other guy was human too. (Ch. 7)
If Pony can see that Socs are just people, the maybe some of the other greasers can too, and the fighting can stop. At the very least, by the end of the book, Pony has turned a new leaf. He has taken Johnny's advice to "stay gold," and put his efforts in education. The Outsiders is proof of that. It is his English paper.
Foreshadowing lets us know what's important, and also adds suspense to a story. When an important event happens, the reader can nod and remember how it was led up to before. Throughout the story, one event leads to another, and everything leads to Pony leaving "the life."