Yank arresting first of hoodlums, ruffian (4)
I believe the answer is:
thug
'ruffian' is the definition.
(thesaurus)
'yank arresting first of hoodlums' is the wordplay.
'yank' becomes 'tug' (I've seen this before).
'arresting' means one lot of letters goes inside another.
'first of' says to take the initial letters.
The initial letter of 'hoodlums' is 'h'.
'tug' going around 'h' is 'THUG'.
(Other definitions for thug that I've seen before include "Brutal criminal" , "Bully" , "Violent hoodlum" , "Violent criminal" , "Violent ruffian" .)