In The Outsiders, what events led up to the moment when Johnny stabbed the Soc?

Previously in the evening, Johnny, Dally and Ponyboy had attended a drive-in movie where they met two Soc girls. One of the girls, Cherry, treats the boys as regular guys instead of as Greasers, and Ponyboy realizes that she is very much unlike the other Soc girls he has encountered. As they leave, they run into two Socs', Randy and Bob--the boyfriends of the two Soc girls--who are not happy about the Greasers being with their girlfriends. Cherry calms Bob down and leaves with him, preventing what could have been a violent situation.

Ponyboy and Johnny aimlessy wander and eventually fall asleep in a vacant lot. When they awake, Ponyboy realizes he will be in trouble with big brother Darry for being out so late. When he arrives home and tries to explain, Darry slaps Ponyboy, who runs out of the house to join Johnny once more.

Johnny tries to calm down the disconsolate Ponyboy as they head toward the local park, which is Greaser territory. Shortly after they get there, Bob and Randy arrive with three Soc friends. All are drunk. As the Socs become more threatening, Johnny becomes frightened. The Socs suddenly pounce upon Ponyboy and try to drown him in the park fountain. Johnny then recognizes Bob--and his ring--as the Soc who had beaten him badly some time before, so he pulls out his switchblade and rushes to defend Ponyboy. Johnny stabs Bob, and the other Socs scatter.