One of the easiest ways of snagging this achievement is to do the optional quest "snatch the snatcher'
This requires hunter rank 3, and will appear under your optional quests.
You'll receive both a trap and a stun grenade for free at the start of the mission. They can be found in the supply chest at Southwest camp.
Once you track the Kulu-Ya-Ku monster, wear him down until he starts to limp ( you'll also receive an audible call out that the monster is ready to capture )
Stand right under the monster, and drop the trap, which will stun it and bring it to the ground. Then use the stun grenade, and the achievement is yours.
It's possible to get the achievement at other times by crafting the traps and stun grenade yourself, but considering you get them for free in this optional quest, you might as well just wait for this.