Players sit approx 10 feet from each other on the floor (depends on the size of the room and the skill of the players). Players alternately flip the bottle caps at each others goal - the cup, which is filled about half way with water (this prevents caps from popping out). If a player makes a shot he scores one point; however the opposing player is allowed the chance to "cancel" the point by making his next shot. If the opposing player misses his cancel shot he is required to take one drink (we generally equate six points to one 12oz beer - no milking). If the opposing player makes his cancel shot, no points are immediately scored. Player one shoots again and if he misses he must drink once (no points). If he makes his second shot it is once again up to player two to cancel - if he misses he drinks twice, if he makes then player one must make or else drink twice. This can go on to the point where a player must chug his whole beer before he can shoot again - only one point is awarded, though.
The only other rule is that any ricochets are worth two points (i.e. a bounce off the floor, or a thigh, or the wall. To cancel, player two must ricochet his cap also. If he just makes a normal shot he cancels out one of the two points and must take a drink.
Games generally go to 15 and you must win by two.
We have played this with as many as four people to a team, or if your room is large enough you can spread individuals into various formations for individual play.
This game was originally played with your beer in the cup that was being shot at - it got pretty disgusting - use the water method. Not only did beer get all over the carpets/floors but whatever was on the carpets/floors got in your beer. Blech.