### Clue: Heavily defeat Right, suffering setback, vitality lacking at first (7)
### Answer: TROUNCE 
 ### Explanation: Definition: Heavily defeat
 **Reversal of**(…, suffering setback) RT(abbrev. for "Right") + "bounce"(vitality/vigour, as in "there was a bit of bounce in his step") **minus its 1st letter**(lacking at first)