Final answer:
Tom Robinson's left arm is injured and has limited use due to an accident he had as a child. This injury becomes a crucial point in the trial, as it is used as evidence to support Tom's innocence.
Step-by-step explanation:
Tom Robinson's left arm is injured and has limited use due to an accident he had as a child. In Harper Lee's novel To Kill a Mockingbird, it is mentioned that Tom's arm got caught in a cotton gin when he was young, causing the muscles in his left hand and arm to be damaged. This injury is significant in the trial of Tom Robinson, as it is used as evidence to suggest that he would not have been able to physically assault Mayella Ewell.