Lobster perhaps reddish-brown: serve in tin (10)
I believe the answer is:
crustacean
'lobster perhaps' is the definition.
(lobster is a kind of crustacean)
'reddish-brown serve in tin' is the wordplay.
'reddish-brown' becomes 'rust' (I've seen this in another clue).
'serve' becomes 'ace' (type of tennis serve).
'in' means one lot of letters goes inside another.
'tin' becomes 'can' (synonyms).
'rust'+'ace'='rustace'
'rustace' placed into 'can' is 'CRUSTACEAN'.
(Other definitions for crustacean that I've seen before include "Hard-shelled arthropod" , "Animal like a crab" , "life form with hard case" , "Such as a barnacle" , "Perhaps crab" .)