Pitch exercises interrupted by breather (6)
I believe the answer is:
plunge
'pitch' is the definition.
(I've seen this before)
'exercises interrupted by breather' is the wordplay.
'exercises' becomes 'pe'.
'interrupted by' is an insertion indicator.
'breather' becomes 'lung' (I've seen this before).
'pe' placed around 'lung' is 'PLUNGE'.
(Other definitions for plunge that I've seen before include "Nose-dive" , "'Dive, plummet (6)'" , "Sudden drop" , "Jump or dive into water" , "land in water" .)