Move to avoid wife during ball at court (6)
I believe the answer is:
swerve
'move to avoid' is the definition.
'wife during ball at court' is the wordplay.
'wife' becomes 'w' (abbreviation).
'during' means one lot of letters goes inside another.
'ball at court' becomes 'serve' (term on a tennis court).
'w' inserted inside 'serve' is 'SWERVE'.
(Other definitions for swerve that I've seen before include "Turn sharply aside" , "Suddenly move off course" , "Suddenly go off course" , "Change direction abruptly" , "Using spin" .)