Snooker player shortens his equipment to gain power in competition (5,3)
I believe the answer is:
davis cup
'competition' is the definition.
(the Davis Cup is a tennis competition)
'snooker player shortens his equipment to gain power' is the wordplay.
'snooker player' becomes 'Davis' (Steve Davis is a snooker player).
'shortens' means to remove the last letter (I've seen 'shortened' mean this).
'his equipment' becomes 'scu' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to gain' means one lot of letters go next to another.
'power' becomes 'p' (symbol in physics).
'davis' with its final letter removed is 'davi'.
'davi'+'scu'+'p'='DAVIS CUP'
'in' is the link.
(Other definitions for davis cup that I've seen before include "Sets competition" , "Annual tennis team championship award" , "International lawn tennis championship" , "event?" , "International tennis team championship" .)