Small numbers -- in what way is that something bothering restaurant? (2-4)
I believe the answer is:
no-show
'that something bothering restaurant?' is the definition.
(as in a no-show for a restaurant booking)
'small numbers in what way' is the wordplay.
'small numbers' becomes 'nos' (abbreviation for 'numbers').
'in what way' becomes 'how' ('how' can be a synonym of 'in what way').
'nos'+'how'='NO-SHOW'
'is' acts as a link.
(Other definitions for no-show that I've seen before include "Someone who neither keeps nor cancels an engagement" , "Individual neither using nor cancelling a ticket" , "One who fails to arrive" , "Person who fails to cancel -- who's on (anag)" , "Person with reservation not turning up" .)