The OCC is implementing the World Curling Federation and Curling Canada five-rock free guard zone, which started officially this season.
The following explanation of this rule appeared September 19, 2017 on the Grand Slam of Curling website.
What is the 5-rock rule? The “five-rock free guard zone” is simply a variation of the existing standard “four-rock free guard zone” rules. The whole free guard zone concept is relatively new in curling. Before then, in a careful, conservative game of curling, teams could take out guard rocks as quickly as they were placed. This led to a clutter-free game, but also lowscoring, predictable outcomes that weren’t very interesting to spectators.
In the late 1980’s, brothers Russ and Glenn Howard came up with the ”Howard Rule”, which eventually became the “Moncton Rule”, based on a practice drill their team used where the first four rocks in play could not be moved at any point during an end regardless of where they were placed. 2 This kept more rocks in play and made for a more interesting game. A modified version of this was adopted as the four-rock free guard zone for the 1992 Winter Olympics, where curling was a demonstration sport, and by the World Curling federation. In this rule, a takeout cannot be played on any stone sitting outside the house between the tee line up to the nearest hog line (“the free guard zone”) until four rocks have been played.
Teams began to find ways to work around the four-rock rule, however, by “ticking” guards aside, which kept them in play but essentially rendered them useless. The Pinty’s Grand Slam of Curling was the first major organization to experiment with a five-rock free guard zone in December 2011 at the Canadian Open. With more rocks in play, more offence can be generated and fewer blank ends can occur. It also makes it easier for teams to come from behind if they are losing.
The Pinty’s Grand Slam of Curling made the five-rock rule official for all its events during a players’ summit in 2014.