Ladder broken during party -- nonsense (10)
I believe the answer is:
balderdash
'nonsense' is the definition.
(balderdash is a kind of nonsense)
'ladder broken during party' is the wordplay.
'broken' indicates an anagram.
'during' is an insertion indicator.
'party' becomes 'bash' (bash is a kind of party**).
'ladder' anagrammed gives 'lderda'.
'lderda' inserted within 'bash' is 'BALDERDASH'.
(Other definitions for balderdash that I've seen before include "Senseless talk/writing" , "stupid talk" , "Poppycock" , "Twaddle" , "Nonsense" .)