Bring down five hundred and three on slides (8)
I believe the answer is:
dethrone
'bring down' is the definition.
(both can mean to remove from power)
'five hundred and three on slides' is the wordplay.
'five hundred' becomes 'd' (Roman numeral for 500).
'and' means one lot of letters go next to another.
'slides' indicates anagramming the letters (letters slide around).
'three'+'on'='threeon'
'threeon' anagrammed gives 'ethrone'.
'd'+'ethrone'='DETHRONE'
(Other definitions for dethrone that I've seen before include "Remove from rule" , "Remove (king)" , "Remove from seat" , "Remove from power" , "Unseat" .)