No problem, and when you say “what gadget”, do you mean what gadget should you use to knockout players?
Oh never mind, I read it wrong! 
Well.. you could use a variety of gadgets to give to the players, like the snowball launcher, blaster, slingshot, prickler, stone burster, etc.
I would personally recommend you choose an easier to use gadget, as it will make the life of the player much eaiser.
Avoid using the quantum portal or pickaxe, or really any other gadgets that are difficult to hit with or have really slow reload speeds.
For a list of all the gadgets, check out this guide!