Why does meg tackle Charles Wallace?

Meg tackles Charles Wallace in the book "A Wrinkle in Time" because she feels a strong sense of urgency and desperation to protect him from the influence of IT, a malevolent force that has taken control of his mind. She realizes that he is being manipulated and is in danger, and her instinct to save him drives her to physically intervene. This moment highlights Meg's determination and love for her brother, showcasing her willingness to confront danger to save someone she cares about.