Foremost metal in front of gate (7)
I believe the answer is:
leading
'foremost' is the definition.
(I've seen this before)
'metal in front of gate' is the wordplay.
'metal' becomes 'lead' (lead is a kind of metal).
'in front of gate' becomes 'ing' (I can't explain this - if you can you should give a lot more credence to this answer).
'lead'+'ing'='LEADING'
(Other definitions for leading that I've seen before include "In pole position" , "Most important; ahead" , "Principal" , "Main" , "Aligned in front" .)