We're going to break the ending down for you in two different ways. First of all, we have to deal with the protagonist. Although he was in a bad position at the start of the story (he has no money, no food, and Laura is about to die), he is in an even worse position by the end (he's been kicked in the head, and Laura will certainly die). Might he have been better off not playing the bingo game at all?
Then there's the technical component of the ending, meaning the artistry that Ellison puts into it. The last line of the story reads as follows: "He only felt the dull pain exploding in his skull, and he knew even as it slipped out of him that his luck had run out on the stage" (87). Notice how we are completely embroiled in the protagonist's point of view – "he felt only the dull pain exploding in his skull." He didn't see who hit him. Ending in such a fashion, with us experiencing life as the protagonist experiences it, increases our sympathy for the protagonist and his struggles.
We have one more aspect of the ending to address here: "His luck had run out on the stage." The story deftly parallels the typical conclusion of a theatrical show (the curtain coming down on the stage) with the finality of the story itself. See "Setting" for a lengthier discussion of theatrical elements in "King of the Bingo Game."