pearl,he is attacked by the unknown assailant that he stabs.

When Juana realized that her husband killed a man, she believed that the whole thing was because of the pearl and its bad luck.  She wakes Kino up and tries to explain to him that they need to leave.

“Can you understand? You have killed a man. We must go away. They will come for us, can you understand? We must be gone before the daylight comes." (Ch. 5)

It is worth noting that when she finds Kino unconscious and he wakes up disoriented he is not concerned with the body next to him, but instead with where the pearl is.  It has consumed his entire consciousness.  Juana probably thought her husband was dead when she first saw him lying there next to the dead man.  All she saw at first was “two dark figures lying in the path.”  She definitely knew that the pearl was the trouble over which her husband killed the man. 

Superstition aside, Juana is right about one thing.  The pearl is trouble.  This item they thought would make them rich causes them to lose everything.  Because of it, their baby dies, and their lives will never be the same.

Kino had decided to go into the big city to sell his pearl because he felt the local merchants were cheating him --- which they were.  He brings the pearl back to his home, but there are greedy men all around him.  He is attacked that night outside of their home before they go to sleep.  Juana begs him to throw the pearl back into the sea.  He tells her that he is the man of the household, and he will decide what to do with the pearl.  That night, Juana gets up and sneaks out of the house.  Her intent is to throw the pearl back into the sea.  Kino sees her and follows her.  Just as she is about ready to throw the pearl into the sea, he stops her and beats her.

"He struck her in the face with his clenched fist and she fell among the boulders, and he kicked her in the side." (pg 59)

He takes the pearl and this is where he goes through the brush line.  He hears someone in the brush, pulls out his knife, and feels his knife go home.  That means that he knifed whoever was out there. He felt it enter the body.  They knocked him to the ground and went through his clothes looking for the pearl.  However, the pearl had been knocked out of his hand and was laying behind a stone in the pathway. 

In the meantime, Juana gets up and heads toward the house.  Steinbeck spends some time explaining the relationship between a man and woman in this culture of theirs.  As she walks, she finds the pearl in the pathway and picks it up.  Then she sees two dark figures lying in the path. 

"......one was Kino, and the other a stranger with dark shiny fluid leaking from his throat." (pg 60) 

Juana realizes what has happened.  Kino has killed this man. It was a turning point in their lives. 

"All of the time, Juana had been trying to rescue something of the old peace, of the time before the pearl.  But now it was gone, and there was no retrieving it.  And knowing this, she abandoned the past instantly.  There was nothing to do but save themselves." (pg 61)

They decide they have to leave.  Kino knows that his explanation of being attacked will not be believed by the men in the town.  They must flee.  He tells Juana to go back to the house, pack up what they may need, get Coyotito, and meet him at the canoe.  However, when Kino gets to the canoe, he sees that his enemies have punched a big hole in it.

After Kino has killed a man who tried to steal the pearl, Juana spots the pearl on the path behind a rock where she also discovers her husband lying beside a man "with dark shiny fuid leaking from his throat."

All of the time Juana had been trying to rescue somehting of the old peace, of the time before the pearl.  But now it was gone, and there was no retrieving it....There was nothing to do but to save themselves.

• When Juana talks with Kino, she convinces him that no one will believe him if he explains why he killed the man because the men of the city will treat him as a peon. So, he tells her to bring all their corn and he will get the canoe.
• But, a great hole has been knocked in his canoe so that he can go nowhere on the water. "He was an animal now...and he lived only to preserve himself and his family."
• Kino hurries back only to find his house on fire.
• They flee to his brothe's house; he and his wife Apolonia have believed they were burned. But, Kino explains what has happened.
• All day, a day in which the wind rises, Tomas tells his neighbors, "Kino is gone.  If he went to the sea, he is drowned by now."  But, each time Tomas returns, he has something borrowed.  Once he brings a big knife, and Kino's eyes light up.
• Kino's family leave Tomas's house in the night. They thread their way around the edge of the city to the north.
• Kino and Juana and the baby hear the music of evil "And the evils of the night were about them."
• During the day, they take a short rest, but he discovers the three trackers who follow them.  He tries to sweep away their tracks as much as possible. Kino considers letting the trackers have him, but Juana convinces him that they will kill them all.
• Kino suggests that they can lose the trackers by going up into the mountains.  "Kino ran for the high place, as nearly all animals do when they are pursued."
• Still, the three men follow. As darkness falls, Kino observes two sleeping and the third squatted with the gun. 
• He decides that he must kill this man with the gun. He undresses to be darker in the night and lowers himself down the rock like "a slow lizard."  Juana watches like an owl.
• Kino arrives too late as the moon has emerged.  He watches the man with the gun light a cigarette. The man hears the cry of Coyotito, thinking it is perhaps a coyote.  He fires his rifle just as Kino leaps upon him, stabbing him.  Then he beats the second man with the rifle and fires it upon the third man who attempts escape. He is "a terrible machine now."
• Kino then hears the moaning, "the cry of death" from the cave.
• "It was late in the golden afternoon" when Kino and Juana return to the village of LaPaz.  They walk side by side, carrying a limp, small bundle; it is the body of their baby.
• Kino and Juana walk "through the city as though it were not there." Still they walk side by side woodenly past their charred home until they reach the shore.
• Once at the shore, they stop and stare over the Gulf of Mexico. Kino lays down the rifle and pulls from his clothes the great Pearl of the World.  When he looks into it, it is gray and ulcerous. "Evil faces peered from it into his eyes, and he saw the light of burning."
• The pearl, "ugly...gray like a malignant growth" is in Kino's hand.  He offers it to Juana, but holding her dead bundle over her shoulder, she says, "No, you."  Kino draws back his arm and hurls the pearl into the sea.
• For a long time they stand side by side watching where the pearl has gone.

In chapter five, Kino wakes up to witness Juana taking the pearl and heading towards the ocean to dispose of it forever. Aware that his wife is trying to get rid of the pearl, Kino sprints towards her and assaults Juana before she can throw the pearl into the ocean. After striking his wife, Kino is overwhelmed with a feeling of disgust and walks back towards his hut. On his way home, Kino is assaulted a third time in the brush but manages to fight off the attacker. During the struggle, Kino stabs and kills the man but ends up dropping the pearl during the fight. Juana recovers the pearl and revives Kino. Although she is relieved that Kino survived the attack, she realizes that he is a wanted man and will surely be arrested for the murder even though he acted in self-defense. Juana then hides the body in the brush and the couple seeks refuge in Juan Tomas's house after they discover that Kino's canoe is destroyed and their hut is ablaze.

I think your question must refer to a very significant event in the story when Kino kills a man who attacks him. In Chapter V of the novel, Kino follows Juana to the beach where she tries to throw the pearl back into the ocean. After he attacks Juana and takes the pearl from her, Kino is attacked by strangers who come out of the darkness. When he hears them coming, he takes out his knife and stabs one of them. Apparently, the other runs away because after it is over, Juana finds only two men lying on the ground, Kino and "a stranger with dark shiny fluid leaking from his throat." The stranger is dead. This incident becomes very important in the story because Kino and Juana's life in their village is over. They have lost their home. They have to run for their lives