Thing type 311, CTF Blue Flag, is the flag for the blue team in Capture the Flag mode. One member of the red team needs to collect this Thing and run it back to their base without having the blue team take it back. If the blue flag makes it to the red team base (provided that the red flag is at the red base), the red team scores a point.
When holding the flag, players cannot perform their special ability. Getting hurt while holding a flag will result in the flag being dropped. When the flag is dropped, it will stay there for 30 seconds before returning to its base. If a member of the blue team picks it up, it returns back to its base immediately, but red team members can also pick it up again and try to capture it. If a flag falls into a bottomless pit or a sector with the Return Flag sector type, it is automatically returned to its original base.