Means rearranging tennis about the start of the day (7)
I believe the answer is:
intends
'means' is the definition.
('intend' can be a synonym of 'mean')
'rearranging tennis about the start of the day' is the wordplay.
'rearranging' indicates an anagram (I've seen 'rearranged' mean this).
'about' is an insertion indicator.
'the start of' suggests taking the first letters.
The initial letter of 'day' is 'd'.
'tennis' with letters rearranged gives 'intens'.
'intens' placed around 'd' is 'INTENDS'.
(Other definitions for intends that I've seen before include "Plans, means" , "Has as a purpose" , "Aims" .)