on someone's side

idiom

1

: supporting someone in his or her opinion, position, etc.

Are you on my side or his?

Whose side are you on, anyway?

2

: as an advantage

He is not a very tall basketball player, but he does have quickness on his side.

3

: helping someone to succeed

Luck seems to be on your side tonight.

Time is on our side. We may well finish the project on time.