How do I kill players who don't fly throught hoops using elytra?
Solution 1:
I'm not a great Minecraft command guy, but for your problem,you can put barrier blocks around the hoops to make a wall with only the hoop as the way through, then the players who do not fly through the hoop will either die from impact or fall damage. If you want to be 100% let them die, you can put lava on the ground or cobwebs that leads to the void.
I hope this answers your question