Chancey is the dairyman at Mrs. McIntyre's farm. He seems like a laid-back guy at the beginning of the story. He's a loving husband, and he gets along decently with the other workers. To make money on the side, he makes his own booze, a fact that Mrs. Shortley fears Mr. Guizac will learn and report to Mrs. McIntyre. Mr. Shortley is also a veteran of World War I.
After Mrs. Shortley dies, he becomes a sinister character. He blames Mr. Guizac for his wife's death and effectively persecutes him by exploiting the anti-immigrant sentiment already present in the community and on the farm. Whether or not he plans for the tractor to crush Mr. Guizac is up for debate. The text leaves that open. But, his silence is not open for debate. Like Mrs. McIntyre and Sulk, he deliberately fails to warn Mr. Guizac of the danger.
What do you make of the fact that Mr. Shortley leaves the farm just after this awful event? Does he regret his behavior? Is he just trying forget what he's done and escape blame? Why might O'Connor have left this open-ended?