Jumped in after taking a breather during exercise. Then departs (7)
I believe the answer is:
plunged
'jumped in' is the definition.
(plunge can mean to jump or drive)
'breather during exercise then departs' is the wordplay.
'breather' becomes 'lung' (you breathe with your lungs).
'during' indicates putting letters inside.
'exercise' becomes 'pe' (Physical Education).
'then' says to put letters next to each other.
'departs' becomes 'd' (common abbreviation e.g. train timetables).
'lung' inserted within 'pe' is 'plunge'.
'plunge'+'d'='PLUNGED'
'after taking a' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for plunged that I've seen before include "Immersed" , "Dived" , "Dove in US" .)