They don't worry the steeple jack - he has bad sight (7)
I believe the answer is:
heights
'they don't worry the steeple jack he has bad sight' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'he has bad sight' is the wordplay.
'has' means one lot of letters go next to another.
'bad' indicates an anagram.
'sight' anagrammed gives 'ights'.
'he'+'ights'='HEIGHTS'
Can you help me to learn more?
(Other definitions for heights that I've seen before include "High places" , "Peaks" , "See 23 ac" , "Distances from top to bottom" , "Summits" .)