Keepaway is the Capture the Flag variant of Halo Wars which shipped with the Strategic Options DLC. It can be played 1v1 or 2v2, although the population is normally low because of the few people who purchased the map pack. This gamemode greatly differs from the variant of the Halo Trilogy.
First off, there always is just 1 flag on the map, which is 'held' by a Protector Sentinel. One only has to approach it to capture it, but the player needs to hold it for 1 minute before being captured. If the unit holding the flag is destroyed or killed, the flag resets and will appear after a while on a random place on the map.
It is unwise to send an unupgraded Warthog to the flag and racing away, because it is easily destroyed. The setup mostly used in the beginning is a couple of ground troups (Jackals or Marines) and some aircraft (Banshees or Hornets). Later on, stronger and/or faster units can be used.