stand up with

verb3

1. •
   To publicly support (someone).

   • [I]t was important as a woman to stand up with other women and raise our voices against the injustice. — 2001
2. •
   In a wedding ceremony, to serve as best man or as maid of honor or as an official witness for (someone).

   • Mrs. Herbert Schmidt, of Hoboken, acted as bridesmaid. . . . Edwin Scheuine stood up with Rudy. — 1931
3. •
   (no longer used) To begin to dance with (someone); to dance with (someone).

   • Joan had not danced with anybody else that evening. . . . Not a man in Lyall's house that night but grudged him the privilege of standing up with Joan Shelley. — 1909