Paddock below the colliery is a dangerous place (4,5)
I believe the answer is:
mine field
'a dangerous place' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'paddock below the colliery' is the wordplay.
'paddock' becomes 'field' (I can't explain this - if you can you should give a lot more credence to this answer).
'below' says to put letters next to each other (in a down clue, some letters go below others).
'the colliery' becomes 'mine' (a colliery is a coal mine).
'field' put after 'mine' is 'MINE-FIELD'.
'is' acts as a link.
Can you help me to learn more?
(Another definition for mine field that I've seen is " Ground too treacherous underfoot".)