The best way to trap any Dino in the game is to build a trap. You will then want to lure it in. If you put a ladder on the back and a cat walk on top you will be able to shoot down on to it. Once that is done climb down into your put on kib and narcos build a chair and sit.once you have done tamed do not destroy your creation later in the game you will want more either for yourself or to trade/sell.
DO NOT listen to the person who wrote the following comment: “DO NOT tame in the lower south cave. It will get stuck on the way out and be trapped there forever.”. If it can’t (which will most likely be the case if tamed down there, because (in my experience) Sarcos struggle just entering the cave with how wide they are. But don’t listen to that guy. Just summon it out in the “Request Creature” tab and wait for it to teleport (I have summoned creatures out of the cave when they get stuck and they teleport just fine). Share this with anyone you know who struggles with that.
Just keep a slight distance away and shoot narco arrows into it's head. If you upgrade your movement speed some (idk how much exactly), you could just keep walking backwards to keep the sarco from reaching you since it never runs on land (at least none of them ever did for me).
I recommend taming one, they are super fast in the water, and they do a LOT of damage. I have tamed carnos and therizos but my one Sarco is the strongest one, I easily killed a megalodon and mine is only level 25, I only leveled up the stamina, speed and melee strength. Knocking it put is easy, just get it to follow you on land then throw some tranq arrows or darts to knock it out and feed it raw meat