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Tuesday, December 20, 2011

A More Offensive Game of Curling – Part I

The BDO Canadian Open has come and gone, but we can only hope its new version of curling is not forgotten.  Mike McEwen and his rink from Winnipeg won the event, the cash and the somewhat controversial CTRS (Canadian Team Ranking System) points,1 which move them further ahead in their quest for an Olympic Trials berth.  What the fans won was a possible glimpse into the future of the sport. 

To the best of my limited knowledge, use of a 5-Rock Free Guard Zone (FGZ) rule in the BDO was the first for a Grand Slam, WCT, CCA, ICF, WCF, or any other sanctioned curling event.  This rule prohibits a team from removing an opponent’s rock in the FGZ area (between hog and rings) until the 6th rock of an end. 

I initially felt the 5-rock FGZ rule would have a minimal impact.  Looking at outcomes based on scoreboard, with an albeit small sample size, it appears I was right.  5-Rock FGZ had minimal impact on outcomes, but what it did have was entertainment impact for the fan.  For those who missed the televised games, the archived video can be seen at  I have only to draw your attention to the final end between Howard and Stoughton in the Semi-Finals where, leading by 2, Stoughton needed to make a double on his first stone to ensure a victory.  There was some risk during the end of Jeff possibly surrendering a three to lose.  It didn’t happen, but the drama was much higher than that of a 2 up final end in a 4-Rock FGZ game.  During Stoughton’s Quarterfinal and Final game, where the winning team was up three in the final end, you’d think twice before turning the channel.  At this level of skill, this usually is not the case.

Some players may dislike the 5-Rock FGZ because it doesn’t reward a team’s good play.  Make all your shots, solid play for 7 ends to build up a two point lead, then one critical miss in the late stages and you could give 3 back and lose.  I can empathize with this point of view.  A team holding a two point lead without hammer in 4-Rock FGZ wins 85% of the time with two ends to play and 88% with one to play.  A visiting baseball team leading by two runs in the 9th inning wins 86% of the time and 89% when at home.   Strong play through 8 innings (similar to 7 or 9 ends) is rewarded with a high probability of success.  5-Rock FGZ feels like the team behind is allowed to put a runner at second base before starting the inning.  I agree, it seems unfair.  But it is fun to watch and I’ll argue the other side.

I wrote years ago about curling as a Battle for Hammer.  What I discovered was, the great play of forcing a team to one was, statistically speaking, no big deal.  In every case (except the last end) in which a team is tied and forces their opponent to one point, the team (now one down with hammer) has increased their chances by no more than 4%, and usually 3% or less.  Similar numbers for being down two with hammer versus one down without hammer (0-3.5% difference). This is why comebacks in curling can be difficult; you eat up ends just trying to get the hammer back, and give up a point to your opponent in the process.  Let’s look at a common scenario in an 8 end game:

First end, you miss a half shot and give up two.  Second end take 1.  You’re down one without hammer and only 6 ends remain.  You are able to get a force in the 3rd end and now are back to two down.  In order to get back into this game, you must score two in 4, force one in 5, score two in 6 and force in 7. That gets you tied coming home.  To get this result you must play extremely well.  However, even if you play well but your opponent matches you, this outcome is not likely to occur.  This is how down two after the first end against the best teams in the world usually leads to a loss.  Going back to our baseball comparison, teams up two runs after the 2nd inning win 66%.  In curling its 74%, and for the top teams its 85-90%.  Even allowing for a large portion of these wins coming against weaker teams, when watching a curling game we may want to flip the channel after the first end deuce.  I wouldn‘t leave a 2-0 baseball game in the second inning, though I may grab an extra beer and try to take a nap

I’m the first to admit one event produces only small sample sizes and we need further games to provide more analysis, but I did compare the numbers from this weekend’s 5-Rock FGZ BDO event to the previous Grand Slam, the GP World Cup.  What did I notice?

  • Teams score more (duh).  10.4 pts/game versus 9.85.  1.42 pts per end versus 1.31
  • Less blank ends.  Only 36 total blank ends in the BDO (9.3%) versus 61 (15%) in the WCGP.
  • Teams are forced to one the same amount of time.  Teams scored a single point with hammer 35% in the GPWC and 34% in the BDO.  For as often the extra guard provided more opportunity, teams likely had to bail out and score a single at risk of a steal.
  • Teams don’t score more deuces, but deuces turned into threes.  Teams with hammer scored two or more 33% of the time, same in both events.  However, deuces occurred 25% of the time in the GPWC and 21% during the BDO.  Four or more was still a scarce event (2% GPWC increased to 3% BDO), and threes increased to 9% from 6%.  Note that in both cases the increase is 50% and, though the sample size is small, we should expect an increase in scoring for teams with hammer.
  • Teams steal more points.  Teams stole 1 point 14% and two or more 3.5% (total of 17.5%) in the GPWC and 17% + 5% for 22% steal percentage in the BDO.  The 5-Rock rule doesn’t give any extra advantage from the 4-Rock rule to a team without last rock.  One likely reason for the increase is that teams, knowing they can’t keep the end clean, become more aggressive without hammer and steal more often.  This leads to the next effect…
  • Fewer close games.  During the GPWC, 19 games decided by one point, 9 extra end games and 89% of games went to the 8th end.  Granted, not all one point games are close (some have a team down three score two in the last end), but we can gain some comparison to the BDO with 13 1-point games, 81% reaching the 8th end and only 1 extra end game.  However, stats can’t tell us that
  • The 5-Rock games were more exciting. 
It wasn’t just the novelty and it wasn’t my imagination.  Giving the team with hammer an extra guard, which is most often used when that team is down, creates more excitement.  Period.  Two and three down are no longer reasons to change the channel.  The trade-off could be more games which don’t reach the 8th end, blow-outs after 5 or 6 ends. However, many close 4-Rock FGZ games are, both statistically and in my viewing opinion, not a close as they appear.  I think 5-Rock FGZ would be a rule that improves the game for the fan and would benefit the sport.

The next question to examine is, does 5-Rock FGZ change Win Probability?  Sample sizes are way too small to give us any real insight.  For example, teams leading by one and two in the late ends (6-8) won more often (75%/93%) in the BDO than in the GPWC (61%/80%).  Given the advantage of the extra guard, we’d expect these numbers to be the opposite.  When 3 or more down, teams in the BDO were able to come back, at any time in the game, 3 times out of 72 (4.2%). In the GPWC , teams only led by 3 or more 44 times, but 4 times a team actually came back (9.1%).  More data is clearly needed to provide a proper comparison.  Based on what we saw in all of the televised games, we could expect to see an increase in win percentage for teams down one or two with hammer in the late stages, but I will hold-off judgment until we see more data.  To get more data, we’ll need to adopt the 5-Rock FGZ rule at more events in the future (yes, please!).

So how did teams handle this rule during the event?  I’ll dig into the three televised games and take a look…in Part II.

1 Yes readers, CWM is going to start using footnotes, in order to segue into information which I’m too lazy to thread into the main article. Similar to the process used by the fine writers at In this case, it should be noted that all teams participating in the BDO had to agree to the 5-rock rule in order to allow CTRS points to be awarded. Perhaps surprising that no one opted out, but I expect any team voting NO would go years without anyone buying them a round of drinks.

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