You can perform stealth kills against freakers by crouching and sneaking behind them. They don’t have clear line of sight during the day so they won’t able to notice you unless you make a lot of Noise. You can also throw rocks to distract enemies. The nearest enemy that will be affected by the noise will be highlighted yellow. Avoid throwing rocks in quick succession to avoid revealing your location.
You can even perform stealth takedowns when you’re in front of them or on their side, as long as you catch them by surprise and without them spotting you first. Stealth takedowns can instantly kill freakers and will save you a lot of ammo and preserve your other melee Weapon’s durability.
When trying to sneak behind human enemies, you have to consider that they can get easily spooked and they have good line of sight regardless of the weather or time of day. You also have to watch out for traps and early-warning devices scattered around their camps. You should always use your Survival Vision when sneaking around human camps to see the traps they laid around. You can even deactivate these traps or re-deploy them for your own use.
We have questions and answers related to this topic which may also help you: