Swear at the skinhead interrupting medical treatment (5)
I believe the answer is:
curse
'swear at' is the definition.
(thesaurus)
'the skinhead interrupting medical treatment' is the wordplay.
'the skinhead' becomes 's' (head letter of 'skin').
'interrupting' indicates putting letters inside.
'medical treatment' becomes 'cure'.
's' going inside 'cure' is 'CURSE'.
(Other definitions for curse that I've seen before include "Trouble" , "use bad language" , "Cuss" , "Imprecate" , "Cause of harm or misery" .)