Rowdy Yank put in hospital (4)
I believe the answer is:
thug
'rowdy' is the definition.
(thesaurus)
'yank put in hospital' is the wordplay.
'yank' becomes 'tug' (I've seen this before).
'put in' means one lot of letters goes inside another (instruction to solver).
'hospital' becomes 'h'.
'tug' enclosing 'h' is 'THUG'.
(Other definitions for thug that I've seen before include "Hooligan" , "Burrowing crustacean" , "16 21 [INDIAN IMPORT]" , "Bully" , "Violent criminal" .)