Dog losing lead in skateboard jump (5)
I believe the answer is:
ollie
'skateboard jump' is the definition.
(I've seen this in another clue)
'dog losing lead' is the wordplay.
'dog' becomes 'collie' (collie is a kind of dog).
'losing lead' means to remove the first letter.
'collie' with its first letter removed is 'OLLIE'.
'in' is the link.
(Other definitions for ollie that I've seen before include "jump on board" , "Fellow" , "Stan and --, comedy duo" , "Hardy" .)