Leaving things to chance on witnessing the event (6,4,7)
I believe the answer is:
seeing what happens
'leaving things' is the definition.
I don't know anything about this answer so I can't judge whether this works.
'chance on witnessing the event' is the wordplay.
I cannot really understand how this works, but
'chance' could be 'happen' (happening is a kind of chancing) and 'happen' is located in the answer.
'on' could be 'at' (I've seen this in other clues) and 'at' is present in the answer.
'witnessing' could be 'seeing' ('see' can be a synonym of 'witness') and 'seeing' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'to' acts as a link.
Can you help me to learn more?