Ace lacking in backbone for meeting in Rugby (5)
I believe the answer is:
scrum
'meeting in rugby' is the definition.
(formation of players in rugby)
'ace lacking in backbone' is the wordplay.
'ace' becomes 'a' (abbreviation).
'lacking in' suggests deleting specific letters.
'backbone' becomes 'sacrum' (bone of the back).
'sacrum' with 'a' taken away is 'SCRUM'.
'for' is the link.
(Other definitions for scrum that I've seen before include "packs together" , "Melee" , "riotous struggle" , "Rugby get-together" , "Rugby-players crouch here" .)