Awful ninnies holding power — they fall dramatically (8)
I believe the answer is:
ninepins
'they fall dramatically' is the definition.
(ninepins get bowled over)
'awful ninnies holding power' is the wordplay.
'awful' indicates an anagram.
'holding' means one lot of letters goes inside another.
'power' becomes 'p'.
'ninnies' anagrammed gives 'nineins'.
'nineins' enclosing 'p' is 'NINEPINS'.
(Other definitions for ninepins that I've seen before include "Skittles (IX, not V)" , "Bowling game" , "Skittles, IX objects to be knocked down" , "Bowling targets" , "Form of skittles" .)