You can hold your ground and wait for reinforcements to arrive. One of many common mistakes I see when fighting for the capzones is that our guys - who, let's say, have a majority of men in the capzone for the moment - go around in search for the enemy rather than take the capzone for us first and THEN go out to kill the remainder of the enemy. As the effect we keep losing people, so we don't have a majority needed to capture/hold the capzone and then the enemy is reinforced/even more of our guys die, so we are losing the capzone.
That's how I see it. Maybe I am wrong.
Well from what I have learned, the rear guard should be capping the zone, while the main force holds the approaches to the zone and the assault force pushes to the next objective. When that assault force gets to the next objective, under cover from the main force, it then holds the cap while the main force pushes through to the approaches to that zone. Then the rear guard in the previous zone is free to move forward and assault the zone after that.
The idea is to meet the next spawn wave head on in no man's land, rather than let them get to the cap zone and start camping it too. At any time the whole thing can reverse and steam roller back over previous objectives, if the enemy manages to flank round and get behind.
Of course this requires a whole team to work together, at least in so far as picking one of the two roles and doing it. One is the assault/rear guard role, the other the main force blocking role. The camp and sniper types should be in that force, because their job is to take out the threats to the moving assault force.
The assault force (regardless of weapon) should be using rapid movement to draw fire from the enemy campers, which then exposes them to counter fire from the friendly campers. The friendly campers neutralise or kill the enemy campers, allowing the run and gun assault troops to get in close and dig them out of cover.
The campers should be forming a line from one protected area to the other in front of the zone being capped. They are trying to form a wall of overlapping arcs of fire that no enemy should be able to get through, especially with the friendly assault troops flanking them at the same time.
Once you get going, the enemy should basically be spawning, running to the front line and then dying, while the cappers sit comfortably in peace, behind the front line. If you are really going hard, you'll trap the enemy in spawn and be accused of spawn camping. The game won't last long if you do.