Why is it ironic that the boy catches bill neatly in the eye with a piece of brick in the book ransom of red chief?

It is ironic because initially, the boy is seen as a helpless captive who is being mistreated by Bill and Sam, but when he turns the tables and hits Bill in the eye with a brick, he becomes the aggressor. This reversal of roles is unexpected and humorous, given the boy's innocent appearance at the beginning of the story.