The free guard zone (FGZ) rule was invented to encourage more aggressive play by ensuring that, if a "team
" desires, a "lead’s
" two "stones
" could be in play (and not removed by the opposing team) at the beginning of each "end
". The FGZ can be used effectively by a "team
" without last stone to place "guards
" on or near the "centre line
", in front of the rings, that can be used to promote or draw behind.
This is the official rule taken from "The Rules of Curling" by the World Curling Federation (WCF):
A stone that comes to rest between the tee line and the hog line at the playing end, excluding the house, is deemed to be within an area designated as the FGZ. Also, stones that are in play, on or before the hog line, after striking stones in the FGZ, are deemed to be in the FGZ.
If, prior to the delivery of the sixth stone of an end, a delivered stone causes, either directly or indirectly, an opposition stone to be moved from the FGZ to an out-of-play position, then the delivered stone is removed from play, and any displaced stones are replaced, by the non-offending team, to their positions prior to the violation taking place.
Annotiation to (b): "sixth" stone from season 2018; until season 2017: "fifth" stone