The flag is an objective in the Capture the Flag and Rabbit gametypes. It is picked up by having a player touch the flag. Once picked up, the flag can be carried around. The flag can be dropped when the carrier drops the flag, when the carrier is struck by an Impact Nitron, or the player is slain.
Capture the Flag
Each team spawns with one flag, which can be picked up and carried by a player of the opposite team. The main objective of the game is to grab the flag off of the opposing team's flag-stand and return it to your flag (which must be at your stand; not carried by an enemy player or laying away from the stand), which rewards your team with one point. By default, the first team to 5 points wins the match.
At the start of the game, the flag spawns near the middle of the map. The flag can be picked up and carried, awarding points to the player holding as long as he does so.