Why did Charles Wallace hit the man in a wrinkle in time?

In "A Wrinkle in Time," Charles Wallace hits the man because he instinctively recognizes that the man is not what he appears to be and is a threat to his family's safety. The man, who is actually a manifestation of the dark force known as IT, tries to manipulate and control the children. Charles's action is a moment of defiance against this oppressive force, highlighting his protective instincts and the urgency of their situation.