on someone's side

on (one's) side

Supportive or in aid of one or one's idea, plan, intention, etc. We're all on your side, Jerry. We just want to see this issue resolved as quickly and easily as possible. If she's going to win this case, she'll need one heck of a legal team on her side.
See also: on, side

on someone's side

In support of someone's views or interests, as in I'm glad you're on my side in this debate, or With the Canadians on our side, we should be able to persuade the Mexicans of a North American policy . [1300s]
See also: on, side