That her father is a drunk and has beaten her before.
He wants to show that Bob Ewell is left-handed, which goes along with Heck’s description of Mayella’s injuries. (meaning Bob probably beat up Mayella)
Atticus makes Bob Ewell write his name in court to show that he is left-handed. This is to suggest that Bob Ewell was the one who attacked Mayella Ewell, since the injuries on her face were consistent with a left-handed person.
Atticus' witnesses in the trial of Tom Robinson were Sheriff Heck Tate, Bob Ewell, Mayella Ewell, Tom Robinson, and Atticus himself. Each witness provided their testimony to support their side of the case.
Atticus attempts to establish through Bob Ewell's testimony that Tom Robinson is innocent by exposing inconsistencies and lies in Bob's story. By showing the jury that Bob's account cannot be trusted, Atticus hopes to cast doubt on the prosecution's case and demonstrate Tom's innocence.
At one point in the book, Bob Ewell spits in Atticus's face for humiliating him in court.
In the courthouse, Mr. Ewell confronted Atticus about being threatened during the trial. Atticus remained calm and assured Mr. Ewell that he had no intention of harming him. Mr. Ewell eventually left, feeling humiliated.
When Ewell was on the stand, Atticus asked him to write his name. Signing your name is a habit; you'll always use your dominant hand. Ewell complied, not realizing why Atticus asked for this.
The children internalize Atticus' admonition not to judge someone until they have walked around in that person's skin
Bob after the trial threatens Atticus that he will shoot him. Bob Ewell feels a lot of anger towards Atticus because Atticus humiliated Bob Ewell in his first time in court. Although Bob Ewell did win the case he lost a lot of his little pride he had.
Bob Ewell spits in Atticus' face out of spite and a desire for revenge, as he is angry that Atticus was able to prove his daughter Mayella was lying about the assault. Ewell's pride is wounded, and he seeks to humiliate Atticus as a form of retaliation.
Bob Ewell, who is Mayella's father, beat her up
Bob Ewell had falsely accused Tom Robinson of raping his daughter, Mayella Ewell, which led to Atticus defending Tom in court. This created tension and animosity towards Atticus and his family in their small town.