Some people who play do the side to side movement when they are facing off shooting at people. They do it so well I wonder if there are using a key bind of a programmable mouse or something like that.
It is so fast and exact. I can’t replicate it with the A and D key.
What are they doing?
It’s probably just practice. It’s really not too hard to press A and D rapidly, and some people are just used to pressing their keys really quickly. I guess you could use a hardware based macro since I’m pretty sure EAC blocks software based macros, but it wouldn’t really be necessary. If anything it would be worse than just doing it by hand, you’d have much less control with a macro.
Also keep in mind at a certain point you won’t get any benefit from pressing A and D even faster. It takes time to move your character out of the way after all, and that time is definitely humanely possible
Most of them probably are simply using mouse & keyboard as input, probably started this pervert thingy years ago. Try using this instead of some X-Box-controller, mostly EZ PZ then. If it doesn’t work, this game seems so like scripts, too.
Pro Tip: Most people are right-handed and naturally feel more comfortable strafing to the right while aiming left. Think of trying to throw a football or baseball to your left while you run to the right. Much easier than the contrary. In game, try strafing to the left and practicing your aim while moving the mouse further away from your body rather than pullin’ it in. Might sound crazy, but I swear you’ll catch some people with it. Yeah though, also helps to have crouch bound to an easily accessible key to mix things up while you move around too. I always bind crouch to my side mouse buttons.
If you think thats hard, wait until you get paired with people that randomly crouch/jump/jump crouch in a firefight.
It will drive you insane!
i find the opposite to be true. I prefer strafing to the left while aiming to the right, because when i strafe to the right and aim left, my mouse hits my keyboard and i run out of room 
you don’t want to be picking up your mouse in the middle of a gunfight
Well, that just means your mouse pad isn’t the size of a refrigerator and you must have short, stubby t-rex arms. Another rookie mistake. I’ll forgive you haha. 
Remember that what you see on your screen when you move =/= what they see on their screen when you move.
It might look fast and exact but often times it’s just slow and consistent. They might hold each key for a quarter second and alternate, but when the game is trying to update their movement on your screen, it looks like they’re popping back and forth, especially because you’re doing the same thing.
In general it’s not the best strategy against competent players anyway. People that just spam adadadad are pretty easily screwed up when you just hold your mouse in the average center of their movement, and do longer strafes. The speedy wiggling doesn’t really allow you to strafe your mouse efficiently. It’s best to alternate your strafe plans; do a short wiggly strafe like that, then go to the left for awhile, duck, go left again, go right, wiggle, duck… be unpredictable.
I also like stutter-stepping where you strafe one direction by tapping a key at random intervals instead of holding it down.
But yeah, they’re mostly just using their slight server lag to make themselves look real fast, and if you try and track them, you’ll just lose.
I agree, as the game do movement prediction, what you see isn’t what they really do (as when you have a connection lost, you continue to move in the same direction).
I find this interesting because ADAD-crouch is the go-to gunfighting strat in Planetside 2, and it definitely doesn’t require a macro. I habitually do it in DB from time to time, but I don’t spam it. I switch directions when someone reacts, and throw in a crouch when I take headshots. Very useful for protracted engagements and throwing snipers.