Bhima fomenting in rage giving turns to his fearful mace struck his enemy with it. Crushing Dusasana's dart, that mace came down straight on your son and hit on the head.
आविध्य भीमोऽपि गदां सुघोरां विचिक्षिपे रोषपरीतमूर्तिः। सा तस्य शक्तिं सहसा विरुज्य पुत्रं तवाजौ ताडयामास मूर्ध्नि॥