Exercise too much in clear wet conditions (9)
I believe the answer is:
overtrain
'exercise too much' is the definition.
'clear wet conditions' is the wordplay.
'clear' becomes 'overt' (both can mean apparent or obvious).
'wet conditions' becomes 'rain' (I can't justify this - if you can you should give a lot more credence to this answer).
'overt'+'rain'='OVERTRAIN'
'in' is the link.
Can you help me to learn more?
(Other definitions for overtrain that I've seen before include "Spend too much time on exercises" , "Prepare too hard" , "Run past peak, perhaps" .)