Jump on board, taking lead from dog (5)
I believe the answer is:
ollie
'jump on board' is the definition.
(I've seen this before)
'taking lead from dog' is the wordplay.
'taking lead from' means to remove the first letter.
'dog' becomes 'collie' (collie is a kind of dog).
'collie' with its first letter taken off is 'OLLIE'.
(Other definitions for ollie that I've seen before include "Fellow" , "Hardy" , "Stan and --, comedy duo" , "jump on board" .)