Why does the father of Mayella Ewell decide to pressure her into making false allegations during the trial of Tom Robinson in To Kill a Mockingbird?
Try to give an answer that could be backed up with textual evidence.
Since Atticus proves during the trial that Tom's crippled left arm prevented him from the crimes of which he is accused, it must be assumed that someone else beat Mayella and tried to choke her. Atticus establishes during the trial that Bob Ewell is left-handed, and since he was the only other person present at the time of the assault, the reader must assume that it was Bob who beat his own daughter. Tom testified that as he was trying to run from the Ewell house, Bob cried out,
"... you goddam whore, I'll kill ya."
In order to cover up his own guilt in beating Mayella, Bob concocted the story that Tom had done it, adding that Tom had raped Mayella as well. Bob hated Negroes, and he must have hated the sight of Mayella hugging and kissing Tom; so, in order to protect his family's reputation (or, at least what little there was to protect), Bob convinced Mayella to go along with his version of the events. Mayella was afraid of her father: When Atticus asked Mayella if her father was good to her, she replied,
"He does tollable--'cept when--"
"... Except when he's been drinking?" asked Atticus so gently that Mayella nodded.
It would not have bothered Bob that an innocent Negro faced execution, and Mayella went along with her father's story for her own safety.