Requires a Dummy account or Bots
Open the command console: ESC > Gear Icon > Under the keyboard tab select Advanced > Check off Enable Developer Console
Press the ` button to open the console and type:
map cp_dustbowl; hostname "boost"; sv_lan 0; sv_cheats 0; (I had to input this twice to be detected on my LAN for some reason)
That will create your match. Use any of the Below Commands as needed:
mp_teams_unbalance_limit 0; - Allows you to stack teams
mp_idledealmethod 0; - Used to prevent from being kick for being Idle
mp_idlemaxtime 0; - Used to prevent from being kick for being Idle
mp_maxrounds 142; - Some maps rotate, this keeps it on the same map
tf_bot_add red - Adds Bot to Red team
tf_bot_add blue - Adds Bot to Blue
tf_bot_melee_only 1; - Sets the Bots to only Melee
sv_cheats 1; sv_gravity 1; sv_cheats 0; - Sets Gravity to low
sv_cheats 1; sv_gravity 800; sv_cheats 0; - Sess Gravity back to Normal
sv_cheats 1; nav_generate; sv_cheats 0; - Allows Bots to move on some maps where they dont.
Choose Medic on the Red Team. Add Bots to the Blue team and either use 1 bot on your team or a dummy account for the engineer. Set up a dispenser and just keep working on it while healing with your medic. One bot arrives it should fire at you guys and unlock the achievement.