on side

Related to on side: on site

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
Farlex Dictionary of Idioms.

on side

supporting or part of the same team as someone else.
1997 Spectator And while clearly ‘on side’ with New Labour, he has never been a closely quartered insider.
See also: on, side
Farlex Partner Idioms Dictionary
See also:
  • be on (one's) side
  • be on somebody's side
  • on (one's) side
  • on someone's side
  • on your side
  • a man cannot serve two masters
  • (one's) (true) stripes
  • (one's) true color(s)
  • (one's) true colours
  • be sold on something