Race in turbulent Tiber (5)
I believe the answer is:
tribe
'race' is the definition.
(I've seen this before)
'turbulent tiber' is the wordplay.
'turbulent' indicates anagramming the letters.
'tiber' is an anagram of 'TRIBE'.
'in' acts as a link.
(Other definitions for tribe that I've seen before include "Close-knit social group" , "Traditional social group" , "Division of, eg, North American natives" , "Extended family group" , "Group of related families" .)