It comes up to beat a giant (5)
I believe the answer is:
titan
'a giant' is the definition.
(titans are giant mythological creatures)
'it comes up to beat' is the wordplay.
'comes up to' says the letters should be written in reverse.
'beat' becomes 'tan' (tan can mean to beat or hit).
'it' written backwards gives 'ti'.
'ti'+'tan'='TITAN'
(Other definitions for titan that I've seen before include "Taint (anag.)" , "Goddess" , "Giant god of Greek myth" , "Jolly large figure" , "immense figure" .)