enter the lists
Also, enter the fray. Engage in a fight or competition, as in He said he'd be willing to enter the lists well before the primaries, or Whenever people disagreed, she was eager to enter the fray. The first term uses the noun lists in the sense of "a barrier around the arena enclosing medieval jousting tournaments" and was being used figuratively by the late 1500s. The variant uses fray in the sense of "a noisy skirmish or battle," a usage from the late 1300s.