Why did Uncle Jack spank Scout? What was Atticus' reaction?

Uncle Jack spanked Scout after she had "split my knuckle
to the bone on his (cousin Francis') front teeth." Scout never got along with her cousin
Francis, and when he called Atticus a "nigger-lover," and then repeated the remark to
her, Scout decided to take action. She waited for Franciks to separate himself from Aunt
Alexandra, and then she let him have it. Jack pulled her off him, but when she tried to
run, her uncle spanked her, leaving "seven or eight red
marks."

Atticus wasn't too upset. He chuckled. "She earned
it, so don't feel too remorseful," he told his brother.