Sugriva and Rama made a plan: Sugriva would fight Vali, and Rama would shoot Vali from a hiding place in the bushes.
Sugriva and Vali fought, but Rama couldn't tell who was who, so he didn't shoot.
Sugriva fled, and Vali scoffed.
"You didn't shoot him!" Sugriva said to Rama.
"I couldn't tell you apart," Rama explained.
Sugriva put on a flower-garland and challenged Vali again.
Rama aimed at Vali, shooting an arrow in his back.
Vali fell, fatally wounded.
Vali's wife Tara wept bitterly and cursed Rama. "You will rescue your wife," she said, "but still meet with grief."
Inspired by: Sita: An Illustrated Retelling of the Ramayana by Devdutt Pattanaik
Notes: This story is on p. 175 of the book. In Valmiki's Ramayana, this is the Kishkindha Kanda (Book 4), sarga 12. The duel and its aftermath occupies several chapters in Valmiki, with long discourses by Rama, by Vali, and by Vali's wife Tara.