Unplaced horse (7)
'unplaced horse' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for also-ran that I've seen before include "Of racing horse, not placed in first three" , "Poor performer in race" , "Unplaced horse" , "Not placed among the leaders" , "One of the losers" .)
(Another definition for alsoran that I've seen is " failure?".)