Final answer:
In the novel 'The Outsiders' by S.E. Hinton, Johnny Cade is the surprise participant. Johnny is a member of the greaser gang who unexpectedly commits an act of violence to protect his friend.
Step-by-step explanation:
In the novel The Outsiders by S.E. Hinton, a surprise participant is the character Johnny Cade. Johnny is a member of the greaser gang and is initially portrayed as quiet and timid. However, when the greasers get into a fight with the rival Socs, Johnny ends up killing one of the Socs to protect his friend Ponyboy Curtis. This unexpected act of violence leads Johnny to go on the run with Ponyboy, becoming a central character in the story.