In a hit and stay you remove a stone and stay in its place: contact point, speed, progressions, rules and typical mistakes, with milestones.
The honest answer: a hit and stay is a takeout in which your stone stays where the struck one was. The world federation's rulebook has no definition of its own for it; it contains "hit" (takeout: removing a stone from the playing area by hitting it), "roll" (sideways movement after contact) and "hit and roll" (a stone that knocks out an opponent's stone and then rolls) [1]. The hit and stay is the counterpart of the roll. A club glossary lists it as "hit and stick": a takeout that leaves the played stone on the same line as the removed one, without a roll [2].
Why is that useful? Because after the hit your stone lies in the house as a counter instead of rolling out. How hard is it? You need a reliable takeout and fine feel for speed and contact. There is no timeline.
Success means: the target stone is gone, your stone still lies where it was. That isn't chance but speed and contact point. Define beforehand what is acceptable (a "pro" miss): better your stone stays just short of the target spot than rolls out [4].
To stop a stone on the spot, you hit its nose, i.e., its middle from the thrower's view [3]. A central hit transfers the momentum to the target stone, and yours comes to rest (practice; the sources don't explain the physics). If you hit from the side, you will probably roll away: the roll is, per the glossary, the sideways movement after contact [1].
Milestone: Three of five stones touch the stationary target stone centrally (practice measure).
Takeout speed comes from a short, fast leg push-off: in elite curlers, push-off time was shorter and velocity higher in takeouts than in draws [5]. The heavier the throw, the later you start the push [6]. For the stay you need a speed that is just enough to clear the target stone, no more.
Milestone: The target stone is gone in three of five cases, and your stone lies in the house (practice measure).
Keep the stone ahead; it is the furthest point forward during the push [6]. Whoever overtakes the stone loses the feel for speed, and without it the stay won't work.
The team can sweep the stone on its way to the target if you are too slow. Your team may sweep the delivered stone anywhere in front of the tee line at the playing end [1], and sweeping can make it travel further [7]. The skip calls. Sweep too much and you roll out.
Remove the higher (front) stone, unless you have the hammer [4]. And don't do the opponent's work: a takeout at the front of the house can push their stone against yours and tip the end in their favour [4].
Practise the stay with a fixed target: a marked stone in the house and a broom marking the nose. Practise in three speed levels (light, medium, firm) and note where your stone stays. That replaces instinct with a table. Instinct comes later.
A takeout that leaves the played stone on the same line as the removed one, without a roll [2]. The term isn't in the official glossary; there you find hit and hit and roll [1].
In a hit and roll your stone keeps rolling to a new spot after contact [1]. In a hit and stay it remains where the struck one was [2]. The difference lies in contact point and speed.
The higher (front) one, unless you have the hammer [4]. Avoid shots that can push the opponent's stone against yours and tip the end [4].
As much as needed to clear the target stone, no more. Takeout speed comes from a short, fast leg push-off, later on heavier throws [5][6]. Try it in steps.
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