One rowing area seized by rough Romans (7)
I believe the answer is:
oarsman
'one rowing' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'area seized by rough romans' is the wordplay.
'area' becomes 'a' (maths abbreviation).
'seized by' is an insertion indicator.
'rough' indicates an anagram.
'romans' with letters rearranged gives 'oarsmn'.
'a' inserted inside 'oarsmn' is 'OARSMAN'.
Can you help me to learn more?
(Other definitions for oarsman that I've seen before include "A male small boat propeller" , "He rows" , "One pulling in boat" , "One in an eight?" , "A ransom (anag)" .)