In Chapter One of S. E. Hinton's novel The Outsiders, the story's 14-year-old protagonist and narrator, Ponyboy, is describing his life on the lower end of the town's socioeconomic spectrum while walking home from a movie. In addition to describing his two older brothers, Darryl and Sodapop, and the group of boys with which he hangs out, Ponyboy also discusses the perpetual state of conflict existing between these boys from broken and dysfunctional homes on one side and the upper-class "Socs" with whom they regularly do battle on the other side. Ponyboy is walking home alone—a risky adventure, he acknowledges ("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")—and, sure enough, he spots a red Corvair following him. The Corvair is owned by a Soc, and its occupants, it becomes rapidly clear, intend to attack Ponyboy, one of them yelling out, "Hey, grease. . . . We're gonna do you a favor, greaser. We're gonna cut all that long greasy hair off." A second Soc pulls out a knife and moves toward the frightened teenager.
Ponyboy finds himself trapped, and he is soon assaulted, pinned to the ground by the knife-wielding attackers. He is saved, however, by his loud cries for help, which bring his oldest and toughest brother, Darryl, to his rescue. The Socs flee before Darryl can get there, but Ponyboy is spared a serious injury at the hands of the Socs.
Ponyboy was assaulted by the Socs, short for "Socials," merely because of his identification as a Greaser. The Socs are arrogant and demeaning, with a few notable exceptions, towards the Greasers, and the latter maintain a close unity as a means of self-preservation.
As explained in the above answer, Ponyboy, part of the Greaser gang, is jumped by a group of Socs, a rival gang, on his way home from the cinema, and saved by his brothers and other Greasers.
The incident is important in that it establishes important themes of the book very early on. It shows the never-ending rivalry and violence between two urban youth gangs who hail from different social classes and opposite ends of town, and who, moreover, sport different fashions. It is significant that the Socs who attack Ponyboy declare their intention of giving him a haircut, which is a derisive reference to a vital aspect of the Greasers' look: their long hair. In fact, long hair is perhaps the most important visual marker of a Greaser's identity. The Socs scorn this look and the Greasers' lower-class status, while priding themselves on being smarter, richer, and more sophisticated.
Gang loyalty as well as well as gang rivalry is also made manifest in this opening incident of the novel. Ponyboy is rescued by his brothers and other Greasers whom he also regards as family. The appearance of Ponyboy's brothers is also important in itself, as the sometimes volatile relationship between the three brothers is overall a major aspect of the story.
As Ponyboy is walking home from the movies in chapter one he realizes that there is a car that seems to be following him and slowing down. The car eventually stops and a few Socs get out of the car, pull a knife on Ponyboy, and ask him if he needs a haircut. As this happens, Ponyboy's brothers and other greasers save him from any harm from the Socs who were about to beat him up. This happens because the Socs and Greasers do not get along; they are from opposite sides of the town. Ironically, right before Ponyboy is jumped by the Socs he is thinking about how dangerous it is for him to be walking home alone; Darry then yells at him for the same thing after they have him from the Socs.