Preliminary race by rower produces a condition (10)
I believe the answer is:
heatstroke
'a condition' is the definition.
(heatstroke is a kind of condition)
'preliminary race by rower' is the wordplay.
'preliminary race' becomes 'heat' (I've seen this in another clue).
'by' is a charade indicator (letters next to each other).
'rower' becomes 'stroke' (term for a rower).
'heat'+'stroke'='HEATSTROKE'
'produces' is the link.
(Other definitions for heatstroke that I've seen before include "Complaint from Sun" , "Effect of too much sun" , "Sickness" , "holiday upset" , "Kos at three (anag) - cause of high temperature?" .)