Out of bounds, goalie knocked over Blade (4)
I believe the answer is:
epee
'blade' is the definition.
(epee is a kind of blade)
'out of bounds goalie knocked over' is the wordplay.
'out of bounds' says to take the centre (the bounds or edges of the word are removed).
'goalie' becomes 'keeper' (I've seen this before).
'knocked over' is a reversal indicator.
The central letters of 'keeper' are 'eepe'.
'eepe' back-to-front is 'EPEE'.
(Other definitions for epee that I've seen before include "Fencer's weapon" , "Type of sword" , "Duelling weapon" , "Olympic event" , "Fencer's sword" .)