Lean over then tumble - that's the danger (7)
I believe the answer is:
pitfall
'the danger' is the definition.
(I've seen this before)
'lean over then tumble' is the wordplay.
'lean' becomes 'tip' ('tip' can be a synonym of 'lean').
'over' shows that the letters should be reversed in order.
'then' says to put letters next to each other.
'tumble' becomes 'fall' ('fall' can be a synonym of 'tumble').
'tip' back-to-front is 'pit'.
'pit'+'fall'='PITFALL'
'that's' acts as a link.
(Other definitions for pitfall that I've seen before include "Hidden danger or difficulty" , "Unforeseen difficulty" , "Unexpected difficulty or danger" , "Unsuspected danger or difficulty - for miner?" , "Trap in the form of a concealed hole" .)