In this scene, Ponyboy gets jumped by 5 Socs. This happened on the walk home from the theatre, with no other Greasers around him. These Socs want to "cut Pony's hair" but instead, they cut his face.
Here, this is a flashback from when Johnny Cade got jumped, but this was worse than Ponyboy's jumping. Johnny got jumped so bad, he had blood stains throughout his clothes. When three of the Greasers are the first to arrive, more show up, worried for Johnny's health.
When Ponyboy arrives home multiple hours late, Darry is furious. Soda tries to protect him, but it backfires, causing Darry to backhand Ponyboy's face. Afterwards, Ponyboy leaves, feeling like an outcast, to go talk to a friend who feels the same way.