Heavy rain could possibly run into chest (10)
I believe the answer is:
cloudburst
'heavy rain' is the definition.
'could possibly run into chest' is the wordplay.
'possibly' is an anagram indicator.
'run' becomes 'r' (cricket abbreviation).
'into' means one lot of letters goes inside another.
'chest' becomes 'bust' (I've seen this before).
'r' inserted inside 'bust' is 'burst'.
'could' anagrammed gives 'cloud'.
'cloud'+'burst'='CLOUDBURST'
(Other definitions for cloudburst that I've seen before include "sudden shower" , "storm" , "dramatic downfall" , "Sudden, heavy downpour" , "Sudden rainstorm" .)