### Clue: Retiring Welsh runner pursuing clubs in characteristic warm-up gear (9)
### Answer: TRACKSUIT 
 ### Explanation: Definition: warm-up gear
 [ **Reversal of**(Retiring) USK(a river;runner in Wales) **placed after**(pursuing) C(abbrev. for "clubs", the suit in card games) ] **contained in**(in) TRAIT(a distinguishing characteristic).