Weight in opening shot towards net causes deflection (6)
I believe the answer is:
swerve
'deflection' is the definition.
(thesaurus)
'weight in opening shot' is the wordplay.
'weight' becomes 'w' (short for weight).
'in' indicates putting letters inside.
'opening shot' becomes 'serve' (I can't explain this - if you can you should give a lot more credence to this answer).
'w' going inside 'serve' is 'SWERVE'.
'towards net causes' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for swerve that I've seen before include "Abrupt change of course" , "Turn aside from straight course to avoid something (6)" , "Veer wildly" , "Turn suddenly aside from a straight course" , "Abruptly go off course" .)