By the time we reach chapter 8 of Night, Elie's father is coming to the end of his life. Wracked by dysentery for which he's not receiving any treatment, the old man is so seriously ill that the end cannot be far away.

Given that Elie's father is in Auschwitz, he cannot count on any sympathy, either from his fellow inmates or from the SS guards. All the other prisoners in the blockhouse care about is that Elie's father doesn't relieve himself inside. But because the old man's too weak to venture outside, he has no choice.

Focused purely on their own survival, and lacking, as we've seen, any sympathy for the man, a couple of prisoners beat up Elie's father, as they can no longer stand him, and all because he's unable to drag himself outside to answer the call of nature.

Later on, Elie's father is assaulted by an SS officer because he keeps on calling to his son to bring him some water. As we've already seen, Elie's father is seriously ill, and his whole body is burning up due to the effects of dysentery. But the SS officer couldn't care less about the welfare of Elie's father, or any other prisoner for that matter, so he responds to the old man's desperate pleas for water by subjecting him to a violent blow to the head.

Eliezer’s father was physically assaulted twice in Chapter 8. First by his fellow prisoners, who were also sick, and second by an SS officer.

Eliezer’s father suffered from dysentery, and his situation was deteriorating. Eliezer was unable to get a doctor to help. His father grew weaker with each passing moment. It was while he was in this state of weakness that the other sick prisoners attacked him. When Eliezer asked the prisoners why they attacked his father, they stated that he was unable to go outside to relieve himself.

"My son, they are beating me!"
"Who?" I thought he was delirious.
"Him, the Frenchman… and the Pole… They beat me… "
One more stab to the heart, one more reason to hate. One less reason to live.
"Eliezer… Eliezer… tell them not to beat me… I haven't done anything… Why are they beating me?"

. . . Then they got angry; they could not stand my father any longer, they said, because he no longer was able to drag himself outside to relieve himself.

Eliezer’s father was assaulted by the SS officer because he refused to keep quiet. He kept on calling out to his son to bring him some water because he was burning up as the effects of dysentery took their toll. Eliezer’s father died soon after.

"My son, water… I'm burning up… My insides…"
"Silence over there!" barked the officer.
"Eliezer," continued my father, "water…"
The officer came closer and shouted to him to be silent. But my father did not hear. He continued to call me. The officer wielded his club and dealt him a violent blow to the head.

In section eight of Night, Elie's father is very ill. He has dysentery and is so weak that he can't get out of bed. Elie tries to ignore his father's cries, but his guilt gives way to him feeling sorry for his father. He gives his father water and some soup, and feels mad, because he wants to keep the food for himself to keep up his strength. Elie struggles with his own guilt over his feelings towards his father. 

The guard tells Elie that death is not far away, and there is nothing else anyone can do for him. Elie's father cries out to the guard for some water, and the guard yells at him to stop, then goes about beating him on the head. The next morning, Elie wakes and finds out that his father has died and was taken to the crematorium. It was Jan, 29, 1945, not many days until they were to be liberated. Elie feels bad that all he feels is relief now that his father has died.

Elie goes through many different emotions while being a prisoner. The Nazis had stripped the Jews of all their identity, and they took away their ability to feel anything. They had all stopped feeling anything. Elie had stopped feeling the father and son bond, and looked at his father as an obstacle now. With his death, Elie thinks he will be free to just think about himself now, and not have to worry about his father. Little does he realize that these memories will stay with him the rest of his life. He will never be able to forget them, and through his work, we will never be able to forget them, either.

The Jews were constantly being beaten for one thing or another, but in this instance the specific reason is because Elie's father was dying.  He is burning up with fever and is very ill.  The "head of the block" tells Elie that nothing can be done for him and that he needs to look out for himself. Elie's father keeps asking for water.  He is crying and begging for water.  A guard tells him to shut up but he doesn't hear the guard. Again he begs for water, and the guard beats him.  Elie hides and does not say anything for fear of being beaten himself.  When he wakes on "January 29, 1945 his father is gone and another man is in his bunk."