Eric worried about medium felony (5)
I believe the answer is:
crime
'felony' is the definition.
(I've seen this in another clue)
'eric worried about medium' is the wordplay.
'worried' indicates anagramming the letters (worry can mean to interfere with or disturb).
'about' indicates putting letters inside.
'medium' becomes 'm' (as in UK clothing sizes).
'eric' anagrammed gives 'crie'.
'crie' enclosing 'm' is 'CRIME'.
(Other definitions for crime that I've seen before include "they say it doesn't pay" , "Legal offence" , "Felony" , "Wicked deed" , "An act punishable by law" .)