To divide a group of people into teams, as when playing a sport or game. The game hasn't started yet because it's taking those guys forever to choose up!
choose up
Select players and form sides for a game or team, as in Jean was always afraid she'd be last when it was time to choose up. [First half of 1900s]
choose up
v.
To select players and form sides, teams, or some other group for a game or competition: The two captains chose up sides for the baseball game.