1. Infinite Swings. The Striker (the person hitting or "striking" the ball) has no limit on the number of tries to hit the ball. He keeps trying until the ball comes in contact with the stick.
2. Ball Must be Fed Where Striker Wishes. The Feeder (the person throwing or "feeding" the ball to the Striker) must throw the ball where the Striker wants it. If the Striker is unhappy with a Feeder, the Striker may request a new Feeder.
3. Any Hit - RUN! Any time the ball contacts the stick, even a "tip", it is a valid hit and the Striker must run. The ball may be struck anywhere! -- however, see Convention #2 for modifications to this rule. The Runners at the Sanctuaries may begin running as soon as the ball is struck -- whether it is a good hit or an Out doesn't matter, once the Runner begins to run, KEEP GOING!
4. Run Clockwise! Upon hitting the ball, the Striker then must run clockwise around the Sanctuaries. The runner does not need to touch any of the Sanctuaries and may run anywhere as long as he passes outside of each Sanctuary.
5. Striker is Out. The Striker is out if the hit is caught in the air or on one bounce.
6. Runner is Out. The Runner is out if he is plugged (hit with a thrown ball) while running. He is not out if he grasps a Sanctuary (that he hasn't used before - see Rule 7) before he is plugged. Note: the Striker becomes a Runner as soon as he begins running.
7. Sanctuarys Work Once. Once a Runner has touched a Sanctuary, he may not let go of it and then grasp it again - it has been used up for that Runner. (The idea here is that you are hiding -- if you suddenly pop out of hiding, everybody sees where you were hiding and it doesn't do you much good to try to hide there again.)
8. In until Out. A player is "In" until he has been gotten out. This also applies to the Castle - all players who are "In" must remain in the Castle (they are "Defenders"), if they step out they are "Out".
9. Undefended Castle is Vulnerable. If there are no Defenders in the Castle (for instance, the last Defender just struck the ball and is now a Runner) the Attacking team (the team in the outfield) may capture the Castle by plugging the Castle Stone.
10. Everybody Out. The teams change sides when the entire Defending team is Out, or when the Castle has been captured.
11. Two Rounders. If the last Defender hits the ball and makes it all the way back into the Castle in one run (a "Rounder") twice in a row then everyone on his team is back In again.
12. No Blockades. No Attacking team member may get in the way of a Runner in an attempt to prevent him from grasping a Sanctuary or proceeding around the Sanctuaries.

Reference: http://www.chaosmedia.com/Rounders/Rounders.html