With love in his heart, jock will move fast (5)
I believe the answer is:
scoot
'move fast' is the definition.
Although both the answer and definition are verbs in their base form, I cannot understand how one could define the other.
'with love in his heart jock' is the wordplay.
'with' is an insertion indicator.
'love in his heart' becomes 'o' (I can't explain this - if you can you should believe this answer much more).
'jock' becomes 'scot'.
'o' inserted within 'scot' is 'SCOOT'.
'will' is the link.
Can you help me to learn more?
(Other definitions for scoot that I've seen before include "Dart off" , "Depart quickly (does not contain H)" , "Skedaddle" , "Move rapidly" , "Move with a rapid darting motion" .)