Why does Walter throw Mr. Lindner out of the house?
Because Walter has foolishly trusted his friend Willy with some of his insurance money that his mother has entrusted to him, Walter decides that he can recoup his loss by calling Mr. Lindner from the new area where they have looked at a house. When the family hears of Walter's plans, they are livid, feeling that he has surrendered to Mr. Lindner.
Shortly before Lindner arrives, Mama tells Walter,
MAMA I come from five generations....of slaves and sharecroppers, but ain't nobody in my family never let nobody pay 'em no money that was a way of telling us we wasn't fit to walk the earth. We ain't never been that--dead inside.
These words strike hard into Walter's heart; so, when Mr. Lindner arrives, thinking he will return the money along with a payoff to the Youngers, he is friendly, offering to explain the terms of the arrangement, but Walter interrupts,
WALTER We don't want to hear no exact term of no arrangements. I want to know if you got any more to tell us 'bout gettin' together?
As Mr. Lindner goes out the door, Walter slams it with hatred behind him.
At first Walter is debating whether to let Mr. Linder do what he wants and allow their family to be bought out. However, once he understands what his mother had said and the importance of how his family had toiled long and hard to make this family, he changes his mind and decides to occupy the house in the white neighborhood. At first he was ready to grovel but after he realizes the effort his father has made and the importance of the family, he does not let himself be sold out and from this he throws Mr. Linder out of the house when he comes to visit. This showcases how family can overcome any obstacles hindering their way.