Valmiki Ramayana Yuddha Kanda Sarga 97 Shloka 28

तत् then, रक्षः Rakshasa, सुग्रीवेण by Sugriva, समुद्यतम्great effort, तलप्रहारम् slap by the palm, नैपुण्यात् with skill, मोचयित्वा hit, एनम् in that way, मुष्टिना fist, उरसि chest, अताडयत् hit

Virupaksha, escaping the slap of Sugriva with great skill, hit him (Sugriva) on the chest with his fist.