Mount and create good relationship with jumper (3,2,3)

'create good relationship with jumper' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'mount' is the wordplay.
I cannot really see how this works, but
'mount' could be 'getonto' (I've seen this in another clue) and 'getonto' is found in the answer.
A single letter 'p' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...

'and' acts as a link.

Can you help me to learn more?