The portly American's taken away for stealing (5)
I believe the answer is:
theft
'away for stealing' is the definition.
'theft' can be an answer for 'stealing' (synonyms). I'm not certain of the 'away for' bit.
'the portly american's taken' is the wordplay.
'portly' becomes 'fat' (similar in meaning).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'taken' indicates named letters should be taken away.
'fat' with 'a' removed is 'ft'.
'the'+'ft'='THEFT'
Can you help me to learn more?
(Other definitions for theft that I've seen before include "Wrongly taking" , "Act of stealing" , "Pilferage" , "A 19" , "Lifting" .)