Why does Mayella Ewell break into tears at the beginning of her testimony?
When Mayella Ewell begins to testify and Judge Taylor simply asks her to tell the jury what happened, she bursts into tears. When Judge Taylor asks her why she is crying, she claims to be afraid of Atticus and says, "Don’t want him doin‘ me like he done Papa, tryin’ to make him out lefthanded...” She is referring to Atticus's strenuous cross-examination of her father, Bob Ewell, and Atticus's forcing Mr. Ewell to admit that he is ambidextrous and could have hit Mayella with his left hand.
Mayella may be afraid of Atticus, but she may also be crying to get the judge and jury to feel sorry for her. Jem says of Mayella, "She’s got enough sense to get the judge sorry for her." In other words, crying may be a tactic she uses in court to get pity. Perhaps she also feels sorry for the perjured testimony she is about to give, in which she is going to lie and help convince the jury that the innocent Tom Robinson is guilty. Mayella truly cares for Tom, and perhaps she has enough decency to feel sorry for lying, even if she knows that fear of her father and of what the white community would say about her cause her to lie.
Mayella's less than successful court appearance begins when she breaks into tears early in her testimony. She tells Judge Taylor she is afraid of Atticus, and specifically is afraid that he will try to make her look like a liar like he did her father. There is a certain element of comic relief here, as Judge Taylor scratches his head. Scout observes that "It was plain that he had never been confronted with a problem of this kind." Further into her testimony, Scout makes another observation about Mayella, that gives us a bit of insight into her character and/or coping mechanisms:
"Apparently Mayella's recital had given her confidence, but it was not her father's brash kind: there was something stealthy about hers, like a steady eyed cat with a twitchy tail."
At this point, the reader may pause to wonder if the tears early in the monologue were real, or part of Mayella's strategy to do well on the stand and/or avoid another beating by her father.