For those that have watched various national and international curling championships on TV, it should be readily obvious that sweeping is a major part of the game. If you pay close attention you can learn the many intricacies of sweeping and many tricks that elite teams employ to get every advantage that they can out of the sweepers.
Even for curlers at the club level, sweeping is still very important. Aside from the obvious function of clearing debris from the path of the rock, the sweepers are able to affect the trajectory of the rock after it has been released by the thrower. In theory, the sweepers can start sweeping as soon as they want, even before the rock has been released. In practice, however, the sweepers usually begin their job at the hog line.
Many times you will see the skip or the thrower join in the action for various reasons. This is not normally encouraged because the effectiveness of a third sweeper is fairly minimal since they are far away from the rock. Unless there is only one sweeper, the skip should always stay in the house and let the two regular sweepers handle the rock. This is because the skip needs to be watching the line and giving sweepers commands.
The sweepers may sweep the rock for most of the length of the sheet. While the rock is in motion, the sweepers are responsible for judging the speed of the rock. If it is heavy or just right then no sweeping is necessary, but if it is light, the sweepers should just start sweeping; no command is necessary from the skip. In fact, for an experienced team, the skip expects the sweepers to judge every rock like this, while he concentrates on the line and whether the rock is curling too much or not enough. Sweepers will also communicate with their skip to let him know the speed of the rock and where they expect it to end up as it travels down the ice. This is perhaps one of the most advanced functions of the sweepers at the club level and a skill that takes a great deal of practice to get right.
Once the rock crosses the tee line, the throwing team may have only one sweeper sweeping. At this point one sweeper, normally the skip, can sweep an opponent’s rock that is in motion. Each team may, in fact, have a player sweeping the same rock. If multiple rocks are in motion beyond the tee line, each team may again have only one player sweeping, so that player must decide which rock to sweep. Though mix ups sometimes occur, at no time may the sweepers from opposing teams intentionally interfere with each other.
Perhaps the least understood aspect of sweeping is what happens when a rock is burned. If a rock is burned between the hog lines, the practice is for the offending player to declare the infraction and pull the rock off immediately. Once the rock crosses the hog line, the play should be allowed to continue if the burn does not significantly alter the path of the rock. The offending player should still declare the infraction and then it is up to the skip of the non-offending team to decide if they want to play the rocks where they lie or pull the burned rock out of play and replace any moved stones. In the third case, if a rock is burned after the thrown rock hits another rock then they play should be allowed to continue and once it is over, the non-offending team’s skip will decide where any affected rocks would have ended up if the infraction had not taken place.