'backstopped' (from 'backstop') originates from Modern English, formed as a compound of 'back' + 'stop', where 'back' meant 'the rear' and 'stop' meant 'to halt or block'.

'backstop' changed from a Late 19th century American English compound (originally denoting a physical 'stop' at the 'back', e.g., in baseball) and later extended metaphorically to mean a safeguard; the verb form 'to backstop' and adjective 'backstopped' developed from that noun.

Initially, it meant 'a barrier or stopper at the back (especially in baseball)', but over time it evolved into its current meanings of 'a safeguard or guarantee' and 'to provide such a guarantee/support'.