Dashing young man grabs four to go off and have fun (9)
I believe the answer is:
gallivant
'go off and have fun' is the definition.
'dashing young man grabs four' is the wordplay.
'dashing young man' becomes 'gallant'.
'grabs' is an insertion indicator.
'four' becomes 'iv' (roman numeral).
'gallant' placed around 'iv' is 'GALLIVANT'.
'to' is the link.
(Other definitions for gallivant that I've seen before include "go in search of pleasure" , "tour for pleasure" , "play around" , "Go out seeking amusement" , "Wander aimlessly" .)