They happen to have a hole in the middle (6)
I believe the answer is:
events
'they happen' is the definition.
(I've seen this in another clue)
'a hole in the middle' is the wordplay.
I cannot quite see how this works, but
'hole' could be 'vent' (vent is a kind of hole) and 'vent' is found within the answer.
The remaining letters 'es' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'to have' acts as a link.
Can you help me to learn more?
(Other definitions for events that I've seen before include "results" , "Important happenings or incidents" , "They take place" , "matters" , "Occurences, happenings" .)