Careless fellow following German during line dancing (9)
I believe the answer is:
Here is my best explanation:
'careless' is the definition.
('negligent' can be similar in meaning to 'careless')
'fellow following german during line dancing' is the subsidiary indication.
'fellow' becomes 'gent' ('gent' can be a synonym of 'fellow'**).
'following' says to put letters next to each other.
'german' becomes 'g' (abbreviation).
'during' means one lot of letters goes inside another.
'dancing' indicates an anagram.
'line' anagrammed gives 'neli'.
'g' inserted within 'neli' is 'negli'.
'gent' after 'negli' is 'negligent'.
(Other definitions for negligent that I've seen before include "Lax", "Remiss", "Not taking due care", "Not minding", "Failing to take due care", "slack", "sloppy", "careless", "Careless of duties" and "Failing to take proper care".)