Road rage — runs into that unknown person (8)
I believe the answer is:
stranger
'unknown person' is the definition.
(I've seen this before)
'road rage runs into' is the wordplay.
'road' becomes 'st'.
'rage' becomes 'anger' (I've seen this before).
'runs' becomes 'r' (cricket abbreviation).
'into' is an insertion indicator.
'st'+'anger'='stanger'
'stanger' enclosing 'r' is 'STRANGER'.
'that' is the link.
(Other definitions for stranger that I've seen before include "'Weirder, odder (8)'" , "Regrants oddly to person unknown" , "Newcomer, alien" , "The unknown one is more unusual" , "Unfamiliar person" .)