Brief absence when one is below par (3,3)
I believe the answer is:
off day
'brief absence when one' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'below par' is the wordplay.
I cannot quite understand how this works, but
'below par' could be 'off' (I've seen this before) and 'off' is located in the answer.
The remaining letters 'day' 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).
'is' acts as a link.
Can you help me to learn more?
(Other definitions for off day that I've seen before include "when one's not at one's best?" , "Some leave" .)