Showing posts with label purpose. Show all posts
Showing posts with label purpose. Show all posts

Saturday, December 22, 2012

± and beyond

I just had to give it a great title, to see what happens when a computer tries to alphabetize that character.


Right now, individual skater stats usually end with the ±, or plus minus.  That's number of points scored by that skater's team whilst she was on the track, less number of points scored by the other team whilst she was on the track.
  • Advantages
    • Easy to understand: a skater with a positive helped her team win, a skater with a zero just broke even.
    • Easy to calculate: for-against, could be done without computer assistance.
  • Disadvantages
    • Hard to calculate with: ± is centred on 0, and 0 is very difficult to factor in to future calculations.
    • Boundless: there is no minimum value or maximum value.  Theoretically, a blow-out win could be orchestrated by 1 jammer, who's ± would be something like +80.
In my opinion, those advantages make the ± a great thing for coaches and individual skaters, on a bout-to-bout basis.  However, it's not as easy for derby journalists, statisticians, and fans of the game.


For those groups, there is another option: the jamming/blocking average.  This is the percentage of points that were scored whilst the skater was on the track, that were scored for that skater's team.  Thus, if the jam score was 4 to 1, the lead jammer's jamming average would be .800 and the other jammer's would be .200.
  • Advantages
    • Easy to use for calculations: it's centred at .5, so a 0 is exceedingly rare and refers to 0 impact on the bout.
    • Bounded: all skaters will have a value between 0 and 1.  There is no possible greater or lesser value.
    • Easy to understand: we're used to percentages by now.  A jammer has .525, she just slightly won.  .725, and she's got good control.  Easy!
  • Disadvantage
    • Difficult to calculate: this one requires a computer to come up with.
I think it's a much better option for fans, journalists, and statisticians.  It gives you, at a glance, how much a jammer or blocker affected the scoreboard in her favour.  As well, it can be compared more easily between bouts and skaters.


There is, as well, a third option.  The first two are concerned with every point scored.  What if we instead looked at benchmarks?  (Thanks to The Mighty Bush for help on this one.)
  1. A jammer's job is 1st to get lead jam.  Thus, let's look at the percentage of jams where a jammer got lead.
  2. A lead jammer's job is to record a full pass, denying her opponent any points.  Thus, let's look at the percent of lead jams where the lead jammer scored at least 4 points more than her opponent.
  3. A non-lead jammer's job is to deny a full pass to her opponent.  Thus, let's look at the percent of non-lead jams where the lead jammer scored less than 4 net points.
  • Advantages
    • Easily to understand: this battery of three stats tell right away how successful a jammer is at those three aspects of the game.
    • Bounded and easy for calculations: centred at .5, bounded between 0 and 1, so easy to apply further.
  • Disadvantage
    • Difficult to calculate: this one definitely requires a computer to calculate all the "if...then..." portions.
This option is great for coaches and skaters, as it gives simple yet detailed feedback on three vital aspects of the game.  As well, it's great for journalists, statisticians, and fans as it breaks down a bout and can give a great "why" for a team's success/failure.


So, there are a few good options to measure jammers.  How to measure blockers?  Maybe later I'll argue for why I like to use the exact same metrics to measure their performance.  What do people think?

Thursday, October 11, 2012

Lost Tactics

There are a few things that have, sadly, disappeared from the game of roller derby.  Without a doubt, the sport is improving as skaters get better by leaps and bounds, coaches discover new strategies, and referees hone their craft harder all the time.

However, I've been watching derby for 5 years now, and there are things I loved to see in the game when I first started that have sadly gone by the wayside.


The Assist

Jammers run out of "juice" during a bout.  Why not help 'em?

By assist here, I specifically mean the whip.  Inside whips, outside whips, hip whips, even the egg-beater.  Ever want to drive a crowd into conniptions?  Use an egg-beater.

Simply, where have whips gone?  Well, all the various leagues I've worked with have been focussed on "defence first" for their blockers.  When there's offensive assistance, it's usually one blocker acting as a screen for the jammer.  This is helpful, no doubt, but it usually works best on the initial pass.  Most jams' initial passes have one team with a 4-wall at the front and the other with a 4-wall at the back, thus a single screen can get a jammer past 2 or 3 blockers.

However, when the play breaks down on the initial pass or frequently on a scoring pass, there's often one friendly blocker and one opposing blocker near the front of the pack.
In this situation, the pink blocker might normally simply block the green pivot to the outside.  Should this block flatten the pivot, then the jammer's home free.  However, should the pink blocker merely surge or screen the pivot to the outside, they may become free to chase the jammer out toward the front.

This is whip time.  Without assistance, the jammer is limited to her own acceleration, which is similar to the pivot.  However, with a whip, that jammer can get much, much higher acceleration and have the pivot beat before she can even start to chase.

I have seen this scenario time and time again in bouts, but the blocker doesn't offer a whip, and the jammer doesn't often take it if offered.  What happens next is the pivot comes forward around the screen and takes the jammer out.  Then she's recycled, etc., etc.

When a jammer comes along, you must whip it.  Whip it good.


The Star Pass

I love the star pass.  It's one of the few opportunities to really take and scramble the plans of an opposing team.  If you watch USARS or MADE derby, which allow the pivot to go and score without passing the star, you'll see that an attacking pivot drives the overall strategy in those rulesets.  However, when I start to talk to teams about the star pass, I always hear the same thing: "But you can't get lead jam status!"

Right, that's true, the star pass isn't right for situations when you consider lead jam status as your #1 priority.  What about those situations where you don't?

  1. Opponents have lead jam
    • Jammer is trapped behind a sturdy wall
  2. In front on a scrum start
  3. On a power jam, with a really knackered jammer
In the first and the third, lead jam is unimportant.  In the first, lead jam's already been conceded.  In the third, the decision's been made to play the power jam to the end, rather than to call it off.  Let's go through them point-by-point.

  1. Lead jam's already been lost.  There's no point in preserving lead jam status, and the jammer's trapped behind a solid wall.  Why not air-lift the jammer out of trouble?  No need to practise the peg assist, just have the pivot slide in front of the wall, then pass the star right over that wall.  Now the pivot-cum-jammer is free to chase the opposing jammer around.

  2. Well, you see the scrum start coming, and your team's stuck at the front.  You've already lost lead jam in this scenario a few times, and so you want to ruin your opponent's positional advantage.  Why not have the pivot line up on the extreme outside, and the jammer right behind her.

    When the jammer whistle goes, the panty can go right over the back wall, and the pivot-cum-jammer is out the front of the pack.  The now ex-jammer is free to help block the opposing jammer.  If the team running the star pass does a great job, the new jammer will have time to come around and score.  If not the jam will be called off, and the team that assumed it had the advantage will be frustrated.  Do this a few times, and they'll be forced to change their tactics.  Congrats, their strategy is fouled.

    Want to be even more clever? There are ways to foul their strategy even more, some involving not even conceding lead jam status.  This I call the option.  The jammer has the option to fake a pass to the pivot and keep the panty, or to pass it off.  As long as the pivot hasn't put it on yet, she can even pass back to the jammer should she get into trouble.

  3. On a power jam, you may want to utilise every second available for scoring, and not call the jam early and "waste" power jam time securing lead jam status for the next jam.  In that case, if the jammer's knackered, it may make sense to simply hand over the panty to the pivot.  Just make sure this is done in the engagement zone but that the panty is on before any opponents are passed.  Otherwise potential points may be missed out on.
If you'd like to read more about the star pass, check out the Team Sealand star pass manual.  This explains the option in even more detail.


I would love to see more teams use these too tactics in bouts.  They would make the sport more exciting to watch, as well as throwing off teams that are too constant in their strategy.  Let's see some clever derby!  Roll on!

Tuesday, September 11, 2012

Tactics Tuesday: Power Jam Offense

I want to talk tactics for a moment.

No, wait, I want to talk plays. There is a difference between strategy, plays, and tactics.

This will be the first of a few entries analysing various popular plays in roller derby. Many people, I think, implement plays simply because they see the big leagues, be it specifically LRG or any other WFTDA side, using them. These plays work in the big leagues, so it's reckoned that they'll work at the local level as well.

Thing is, a play is like a multi-variable function in maths. It operates on a set of initial conditions or parameters, such as the skaters, conditions of the bout, and rules, and produces an output (points). One expects, for a given set of parameters, to see an output within the margin of error. Ever see a bench manager go into an absolute fit, but not at the ref? That's because the function gave an unexpectedly low return.

Monday, September 10, 2012

The Nature of Rankings


I was doing some research last night, and read a number of academic papers on the ranking of sports teams where there is no balanced schedule.  (Balanced schedule meaning that each team plays each other team, like in the Premiership.)

The thing that the articles made me realize is that there is no such thing as a "perfect" ranking scheme.  What would "perfect" mean?  No upsets, maybe?  Well, there will always be upsets in sport, so that really won't work.

Thursday, August 30, 2012

The need for a ladder

With the rise of International Roller Derby, there exists a need to rank the nations.  Roller derby fans want to know which national team could beat which other national team.  That is what we provide here at the Derby Ladder of Nations.

We begin with the rankings as produced by the Blood and Thunder World Cup, which finished on 4th December, 2011:

1USA
2Canada
3England
4Australia
5Finland
6Sweden
7France
8New Zealand
9Germany
10Scotland
11Ireland
12Brazil
13Argentina

Were there to be no further international bouts before the next world cup, these rankings should stand.  However, with England, Finland, and Sweden all due to play the USA this coming weekend, there needs to be a standard system of sorting the teams as a result of these bouts.

This sorting system is the Derby Ladder of Nations.

Stay tuned to find the formula that will be used to find the new rankings at the conclusion of England-USA on Monday, 3rd September.