Pile on to player (7)
I believe the answer is:
reactor
'pile' is the definition.
(I've seen this before)
'on to player' is the wordplay.
'on' becomes 're' ('on' can be mean 'with reference to').
'to player' becomes 'actor' (synonyms).
're'+'actor'='REACTOR'
(Other definitions for reactor that I've seen before include "I swing back" , "Heart of a nuclear power station" , "(Nuclear) powerplant" , "Nuclear energy generator" , "one liable to have a meltdown if things go disastrously?" .)