Positioning and Roles
For this strategy to work, all players must stay on the left side of the map to prevent enemy bots from walking around and attacking players from behind.
The areas of interest in this strategy will be the upper left and upper middle quadrants of the map.
On the red line, heavy barricades should be placed. Shielders should stand on the blue line. Behind the shielders should be skirmishers or commandos with long weapons (I recommend faster weapons that can be used to overhead spam). Ranged players can also fire from the area behind the angled palisade. With this set-up, you can have two or three commandos shielding and 3 melee attackers. Attackers should always stay right in between the openings between shield-bearers.
Deployable shields are placed on the maroon lines so that archers have shields against enemy ranged weapons. Archers can stand on this platform to fire from (preferably the left side and out of view of the main entrance.
It is imperative that there be a full-time medic. The medic can continuously refill medic boxes with the ammo box. Those shielding should refrain from attacking unless it is absolutely safe to attack. In higher waves, I would not recommend attacking even if it seemed safe, as there is a high chance you will die in one hit.
At the start of the round in hard mode, everybody should immediately move to the left side and form a shield line covering the whole expanse. Only until the wave is nearly over should you begin building the barricade.
Note: Enemy ranged bots often get stuck outside, so you may have to have the whole team walk to the right side of the map to lure the bot in.
Shield-bearers should repair their shields at the end of waves, or respawn to acquire fresh shields. Shields picked up from bots are no longer the same strength as player shields.
Hopefully, this guide helps. If there is anything that I have missed, feel free to add corrections. Thanks to the VLKA for showing me this strategy.