To "Sharpshoot" is to make false claims to derail the progress of a game. Such as false claims to extensive knowledge of a topic and experience.
For example; If I post an advert for an "Isekai" adventure using Pathfinder 2e rules and give the following introduction:
Scenarrio outline for players to get the gist of the introduction;
1. A group of attractive college attending young adults in a college study hall,
2. they side step into another room when they are done for the day to try a role playing game.
They are told to make their characters but not to give their characters names. Their characters are meant to be idealized versions of themselves.
3. The GM is secretly a master "Hypnotist" who left vegas. The GM places them all into a hypnotic trance and...
4. The group experiences a role playing game world (*not as a computer game with pop-ups and menus, but as if they are well and truly transported somewhere else)
5. they comeback to the real world and discuss the vividness of the experience,
6. then ask how they ALL could experience EXACTLY the same things,
7. then ponder some fringe areas of psychology/parapsychology/philosophy, shit like "Flat-land" and other dimensions.
8. one player notices the time, despite "being there for a few hours, no time has passed since they actually sat down".
9. One player has "dust" from tree bark all over his hands and shirt.
10. another player has a stinging angry red welt scratch, where his character was hit by an orc.
11. they notice one player, hasn't woken up from the trance.
12. The "What-the-fuck" fight breaks out between the players and the GM.
13. This isn't possible! Get her back! How is she "stuck" in a hypnotic trance? You- YOU DID THIS!
14. GM, "You are the only ones who can go and get her back, and I am the only one who can send you all back there."
15. "We narrowly escaped, do we leave her consciousness trapped in the other world (and as a prisoner of the orcs no less), or"...
16. "When we get back, GM, we are gonna have some words!
A sharpshooter in this scenario would be a player who says, "I am a hypnotist. I know what hypnotism is. I don't allow the hypnotist to hypnotize anyone there." just for starters.
In the above, hypnosis is only used as a plot device and the "handwave-ery" for how the fictional players above travel to a world of fantasy adventure.
This introduction is meant to "open a can of worms so to speak, as it should provoke the players to wonder, investigation, exploration, and looking for answers.