Bob Ewell, who is Mayella's father, beat her up
Her father, Bob Ewell.
Actually, Atticus doesnt mock Mayella. Mayella thinks Atticus is mocking her because he is caller her Ma'am and Miss Mayella, which she isnt used to.
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Atticus suggested that Mayella Ewell was likely injured by someone left-handed based on the bruises on her face. He believed it was her father, Bob Ewell, who was left-handed and had a history of being abusive towards his daughter.
Atticus wanted the jury to have a picture of Mayella's life because he was trying to get everyone to see that she has to do all the chores, and she like the "outcast" of the family. He was also trying to show that Bob Ewell gets mad and drunk a lot at Mayella. And that is how she gets beat, and raped.
When Mayella is on the stand the question Atticus asks that makes her furious is "How?" She has just described how Tom Robinson choked and beat her, and Atticus asks Tom to stand up. This draws the jury's attention to the fact that Tom's left arm is useless, making it highly unlikely he was Mayella's attacker. When Tom stands, Atticus asks Mayella if Tom is the man who attacked. When she responds that he is, Atticus asks, "How?"
Atticus suggested that Bob Ewell, Mayella's father, was responsible for hurting her. He argued that Bob Ewell abused and manipulated his daughter as a way to cover up his own actions.
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)
The judge asks Mayella what she's scared of, and she points to Atticus
Mayella cries because she thinks Atticus will find out that her father really did it.
Bob Ewell or Mayella
"Tempting a Negro"