Why did tom kill a man outside of the keene ranch in The Grapes of Wrath by John Steinbeck?

In "The Grapes of Wrath," Tom Joad kills a man outside the Keene ranch in self-defense during a confrontation. The man, who is a former associate of Tom's, attacks him with a knife after a heated argument about the treatment of migrant workers. In the struggle, Tom strikes back, resulting in the man's death. This act underscores the desperation and violence faced by the characters in their fight for survival amid social injustice.