Left 4 Dead

It's best to do this achievement with the AI as they rarely dole out any friendly fire damage and you don't have to deal with a group that may be mistake prone. Set the difficulty to easy and play whatever campaign you're most comfortable with. Be selective with your shots and let the AI do most of the work. I suggest using a sniper or pistol so you don't start spraying and unintentionally hit a teammate, who have a tendency to walk in front of you as you are shooting. Obviously, melee as much as possible to avoid any incidents. The achievement will unlock about 5 seconds before the credits start rolling.

Please note that many people have reported that this achievement will not unlock upon meeting the requirements on the Crash Course DLC.

The AI can get friendly fire very very rarely, but not from shooting you, so don't worry about them shooting you.

Just play solo on easy.

Don't use any weapons but the pistols and hunting rifle, not even miniguns.
Don't use molotovs or pipe bombs unless you KNOW you can toss one safely.
Never shoot when the team is holed up in a corner. (They can clip through you and get shot.)

Crouch and melee attack to let the AI shoot over you. Remember you're only job is to survive, not to actually kill infected. So don't even shoot most of the time.

You should only ever shoot in two situations.

#1 When any teammate is off screen you should be moving away from them so that they cannot run into your line of fire, if they're behind you this means moving forward.

#2 When all teammates are on screen so you can watch their movements and make sure they don't run into your line of fire.

In either case only shoot if you have a 100% clear shot.

Run past witches without disturbing them if you can.
Run away from the tank and let the AI's handle him.

Avoid shooting or standing near gas cans that the AI might shoot yes if they walk into a fire all on their own it still counts as friendly fire. It may be best to shoot them out before getting to them or move them to safe places for crescendo events.

If you do No Mercy on the first level hop onto the ledge at the back of the building and run (don't jump) across to the air conditioners. You will only take 17 damage and skip the whole apartments. Drop to the alley and clear it, your AI buddies will run the entire apartments in about 20 or 30 seconds and join you. You can also try speedrunning the whole map instead of waiting. No AI's around means no FF and if they die you get them back on the next map anyway.

During horde attacks find a corner and just crouch and melee, your ai's will do the work. The AI's don't follow you into rooms and closets very well so corners work better.

For the finale get outside and run around buildings to stay away from the tank. Only take careful shots you know won't hit team mates. After the second tank falls run for the chopper right away so you won't need to use a pipe. Don't use a molly on the tank up on the room because the AI's will scatter in every direction and run through it.

Remember, do NOT shoot a team mate. This rule is more important than anything, even surviving. If you die you can just restart the map. If you shoot someone you have to exit out to the menu and restart the entire campaign from the beginning. (Do NOT vote to restart the campaign, you still won't get the achievement even though it will say no FF in credits.)

Now for the good news. If a teammate is pounced or smoked they cannot take FF, go ahead and shoot if the others are clear. BUT, if you are close enough to melee instead do that. Melee is superior and in solo there's no melee fatigue so abuse it.

Mines, a lot like AbsolutelyBaked. Set Difficulty to Easy. The achievement icon has a rifle in it. Yes it. Use the rifle all 5 levels. With the rifle you're less likely to hit a survivor. Also, let other survivors do most of the work. The survivors don't move forward until you do. So, what I did was move forward a bit into a crowd of infects then run back behind the survivors. Most of the time granted there are no special infected, they'll take them all down. Another thing that helped was melee. Melee most of the infected's (which may even get you Spinal Tap achievement) and let the survivors behind you take'em out.

Like has already been stated, set difficulty to EASY. Stay crouched and stick to MELEE attacks. I've personally found it best to NOT pick up any weapons at all. Just stick with pistols and use them ONLY when nesssecary, i.e. vs. a tank. Be sure to avoid moving around alot when dealing with an incoming attack as you might inadvertantly step into an ally's line of fire.

Simply play solo on easy (any campaign) and melee with a health pack from beginning to end. Use pipe bombs and Molotov's when needed. Speed run for an easy 30.

I find this easiest to do on Dead Air. I didnt fire a single shot the entire campaign. Easy mode, 3 computers, only pick up pills, medkits, and pipebombs. Dont risk setting them on fire from molotolv. Dont use a shotgun, uzi, assault rifle, or hunting rifle. Only Dual Pistols. If you dont have Akimbo Assasin, this will also give you that.

The easiest way to do it is to follow all previous advice (go through the level with all AI on easy and only bash) and do it on the crash course campaign. With the crash course campaign, it takes a hell of a lot shorter time and you can also kill two birds with one stone by going for the littlest genocide achievement at the same time. Hope this helps.

To add on to the advice above, one extra tip (if you have downloaded it) is to play the Crash Course campaign. It's only two episodes long and is obviously shorter in length, meaning less chances to shoot your teammates. This also counts towards any achievement that specifies you have to survive an entire campaign whilst doing something, such as Akimbo Assasin, and ensuring a boomer doesn't vomit on your etc, or completing a campaign without being healed, completing a campaign on expert...you get the drift.

This one's kinda difficult, not gonna lie... But believe it or not, it's MUCH easier with the AI. The AI almost never friendly fire. I'm not gonna say it's impossible for them to friendly fire, but I've never seen it happen. Make sure that you don't friendly fire either. The best way is to use a pistol the whole time. Works well with:



Double pistols works too. The fire isn't very scattered and makes things much easier. The hunting rifle also works (the achievement picture even tries to give a hint, but I go with pistols since there's an achievement for it.)

If you ever see a circle with a slash through it saying "do not shoot other teammates" (or something along those lines), then you've friendly fired and have to restart the whole campaign in order to try for this achievement again. Just resist the urge to pick anything up (I do not know if it voids the Akimbo Assassin achievement to carry another gun, so I just wouldn't).

This one is a little more advanced though, just remember:

-Go on easy on single player
-Run through with only pistols
-Be very careful when shooting.
-Only shoot when absolutely necessary.
-Melee when in close corners or boomed on to prevent accidental shooting.

Also:

The achievement description can be misleading because on Easy, it's impossible to take damage from friendly fire, but ANY friendly fire voids this one, whether you take damage or not.

The best way to get this one is using the sniper rifle just against the tank, in other infected just use the pistols, but make sure that none of the bots of friends are in your sight, I highly recommend you to just melee any zombies or special infected, avoid the witch, and the most important thing you have to be very careful with pipe bombs, molotov cocktails, gas tanks and propane tanks because any of this explotions or fire are considered by the game director(computer) as friendly fire. have fun : )

AI rarely cause friendly fire damage, although it is possible when gas or propane tanks go off, or (suposedly) if a Boomer nearby is shot and hits someone. I'm not sure if the covered individual needs to be attacked or not.
If your stray molotov or pipe bomb causes damage it will count against you.
My wife and I did this together.
The best tips I can give are to do it on easy, and allow the AI to handle most of the big obstacles that come your way, including the Tank. Witches can be tricky if they are spawned in a location that the AI can't get around. Blast her in the face with shotgun shells, if you fail to kill her the AI will finish her without hurting you.

Player Tips:
We found out that comunication is very valuable. Tell your partner(s) where you're going and what you're doing. If you see a boomer or other Special Infected in front of you, don't back up while firing or you may accidentally shoot your teammates.

My prefered campaign is No Mercy because of the "Jesus Room" on the Finale.
Don't know what that is? Look it up, it's helpful!

You and 3 friends should start a campaign on Easy. When Chapter 5 begins, have everyone vote to return to the game lobby. Then, begin the same campaign on Easy on Chapter 5. You can do this on any campaign, do whichever you are most comfortable on. Now do not shoot each other. Have one or two people shoot while the others melee infected away. Remember that pipe bombs and molotovs can do massive friendly fire damage. Can also be used to obtain Untouchables, Do Not Disturb, Stomach Upset, Unbreakable, Akimbo Assassin and Stand Tall. Simply fulfill the requirements for each achievement. It also works for the expert achievements.

Personally I went through the No mercy campaign on easy (though i suppose you can do any campaign you want) and didnt do anything except melee. Melees cant land you in a friendly fire situation and the AI will do the rest of the work. Easy achievement. :)

I got this achievement by playing solo No Mercy on easy, used shove when I was close to AI and waited until the 2nd weapons tier for the Hunting Rifle. The most important thing is to let the AI do a lot of the work and shove a lot. Only shoot when the AI are nowhere near where you're shooting or if you can aim around them. It is an easy achievement if done right.

There's the legitimate way of getting this, then there's various glitches you can use if you don't want to get it in a noble fashion.

Legit: I would recommend playing a campaign you know well, in Easy mode, with four human players. Move swiftly with full captions on and simply melee all the way through. Never shoot!

Glitch: There are several, and I'll cover them in detail.

1) Play all the way through an Easy campaign without worrying about friendly fire. Dead Air is probably the best one to do it on. It doesn't matter at all if you get hit by any friendly fire, and you can just play through without worrying about it. You have to have four human players.

Now, when you get to the finale, DO NOT open the opening saferoom door and vote to return to the lobby. Now, in 'Edit Game Settings' change it to chapter 5 (which should be the finale) and start it up again. The reason this works is because the game acknowledges the fact you've played through the whole campaign, but it says you never got incapped, never healed, and so on (so you can unlock several achievements at the same time using this). Quickly rush through to the end of the finale, where the actual finale 'event' take place.

There is actually a glitch to beat every finale without so much as killing a single Infected. On No Mercy you can let zombies break down a door and then go into a room where the AI can't see you, on Dead Air you can jump on top of the plane by moving one or two carts with propane tanks, on Blood Harvest you can actually just stand and melee a tree and everything will immediately die before it reaches you (!) and on Death Toll there's a rock you can sit on. Crash Course, as far as I know, has no finale glitches. But I'm not going into how they work and not saying you have to use them. It has little relevance, just find them out through Google or YouTube.

I hope this helps.

i started with the uzi and went through the no mercy campaign (picked up the hunting rifle when i could). when you shoot, try not to have any of the A.I. in front of you. in a horde or if one of the A.I. is attacked by a hunter, melee. be prepared to waste hours trying to get this one.

an extra thing, try not to use canisters and grenades when near allies, it counts as friendly fire, apparently (i accidentally did this once and it popped up as far as i remember).

Play a campaign on Easy with the AI. I got this achievement as well as the "Akimbo Assassin" (finish a campaign using only pistols) achievement on the same playthrough of a campaign. Try to stay behind the AI when a hoard comes, melee a lot and don't shoot unless you're sure you won't hit any of the AI.

By rights, I should not have this achievement. I was playing Crash Course with the AI's and Louis decided to jump in front of me when I shot a zombie, it even popped up saying "Don't Shoot Teammates" but after the rescue vehicle went, it popped up.

My advice is to do it with AI's as they do not shoot each other or you, you must be very very careful with your shots.

I got this in no mercy campaign on about attempt 4. You could also do this on Crash course if you have it. The main this is NOT THE SHOOTING, BUT THE PIPE BOMBS/MOLOTOVS! I don't know how many times mine bounced and hit them causing quite a bit of damage. Use an UZI/Assault rifle ( Sniper is rubbish ) and just pick off the single zombies. If the AI get too close to you just melee and be patient really this isnt too difficult. Focus on the special infected and on easy the AI should mop up the single zombies before you do. If you do need to throw a pipe bomb / molotov make sure the AI is nowhere near it (pipebombs have a large damage radius). Also DONT PANIC if you hear a tank, it doesnt matter if you die.. just shoot it when the AI arn't near it.

single player on easy. use guns sparingly. comp will never shoot u so let them do all the work. use melee attacks and the comp will finish thm off

We just did this in a different way to the other solutions so felt it was worth a mention.

There were three of us, so two of us went into 'Idle' mode while the third player played through Crash Course and shot very little and did more melee as described above.

Right at the end when the van comes right down and the door opens we went into active mode and hopped in with the active player.

It very much depends on the active player being cautious as described in other solutions but it did mean all three of us popped the achievement at the same time so it's worth doing if you're in a group and you all need to unlock it.