As
the European roller derby scene grows and the skill levels of the top
teams increase, the WFTDA rankings are sure to become a more and more
important indicator, especially as success in those rankings will be
a ticket to a whole new level of game play i.e. the championship
games.
Roller
derby as a sport is going through a period of metamorphosis during
which both international organisations as well as national
associations are trying to find their own place. Even the WFTDA rules
are in competition with other roller derby rule sets but at least we
can say that the teams that play under the WFTDA or MRDA rules have
one thing in common: the rules. Each derby team has a different
season and different culture. Some leagues play interleague bouts
whereas others organize big tournaments or competitive tours. One
thing we know for sure is that everyone wants to be the best. But how
do we measure this?
Considering
that not all leagues and teams, that play under the WFTDA and MRDA
rules, are members of the international governing body and that mixed
teams don’t even have the option of becoming members, it is
difficult to determine how to rank these teams and especially how to
compare the skill levels of the European all-star teams with their
American counterparts. The answer is to develop a ranking-system
based on bouts that the teams play. But because bouts are still
arranged only occasionally and rather irregularly, the teams don’t
necessarily fully know their opponents level and thus bouts may end
up being pretty unequal matched. Therefore, the ranking system can’t
just be based on the score difference. It is also important that the
rankings also support the teams in picking their opponents. As a
result, various ranking-lists have sprung up based on different
formulas and it seems each one of them has something to offer. Some
listings don’t compare the number of bouts won to the number of
bouts played whereas some have split teams into different divisions,
which don’t really reflect reality. At the moment, it seems a lot
of people are talking about WFTDA’s new, division-based ranking
system that also affects the seeding of WFTDA member leagues i.e. how
the tournament places in the championships are distributed. As a
result of the teams being split into different divisions, many teams
are unwilling to play any opponents ranked lower than them because a
surprise victory would mean a big drop in rankings. For example, this
means that it doesn’t make sense for the London Rollergirls’
all-star team to play at all in Europe because LRG is ranked far
above any other European leagues. So why have such a ranking system?
Mathematics
instead of geography
The
teams in the WFTDA championships have so far been selected on the
basis of the leagues’ geographical location and playoff tournaments
in North America. Until now, the playoffs regions were Eastern USA,
Western USA as well as North
Central and South Central USA and, at the WFTDA tournament in each
region, 10 teams competed for three places at the championships,
which are arranged every autumn. The regional split will still remain
as there aren’t sufficiently many European member leagues competing
at the top level to justify setting up a separate Europe-region. The
teams from outside USA will compete in the region that they are
geographically closest to, for example the European teams would
belong in the Eastern region. After the geographical split was set up
and up until 2013, WFTDA used voting-based rankings, which took into
account the bouts each team played over the course of the year, to
determine the placing of teams within a particular region. During
2013, the fully mathematical Competitive Division System stepped into
play with the hopes of some day getting totally rid of the
geography-based system.
Goals
One
of the goals of the new system is to make the bouts tighter by
fostering better matchups. This should enable teams to develop faster
and allow the differences in skill levels to even out. Secondly, the
system is aimed at more precise measurements. If the minimum game
play requirements to make it into a division are higher, there will
be more data and the results will be more accurate. Of course the
reforms also seek to allow room for the number of teams to grow and
foster the geographical spread of the sport. Surely one of the most
important underlying thoughts has been to ensure that the very best
teams will be competing in the finals at the WFTDA championships.
Basic
principles
The
split into divisions is based on the tournament season, which starts
immediately after the WFTDA championship tournament has been played.
The allocation of a team into a certain division for the next season
is determined based on the bouts the team has played during the
previous season. Thus, it is not possible to move up a division in
the middle of the season. The rankings within each division are based
on the bouts played after the WFTDA playoffs (in the autumn) but
before June 30th
next year. The rankings of 30 June will determine how the teams are
placed in the WFTDA playoffs, which will in turn decide the opponents
in the playoffs and in the finals. The teams also need fulfil the
minimum game play requirements by 30 June to qualify for the
tournaments. Just as before, the 12 best teams, three from each
qualifying tournament, will still advance to the finals.
Divisions
The
all-star teams of WFTDA leagues were divided into three divisions in
autumn 2012 based on the bouts played during the previous season.
Division 1 includes the top 40 teams, division 2 consists on the
teams ranked between 41-100 and any teams ranked 101 or lower will
form the third division. New member leagues start their first season
automatically in division 3. To compete for a place in the playoff
tournaments, a team in the third division will need to have played at
least two WFTDA-sanctioned bouts against D1-, D2- or D3-teams. A team
in division 2, on the other hand, will need to have played three
bouts (at least two against D1- or D2-teams but one can be against a
D3-team). The criteria in the first division is even tighter and
these top 40 teams will need play 4 bouts; minimum three bouts need
to be against another division 1 team but one of the bouts can be
against a division 2 team. These requirements thus seek to ensure
sparring opportunities for the teams and decrease the differences in
skill levels between teams. Take London Rollergirls for example, they
are in the first division only preceded by the current WFTDA number
one, a New York team, Gotham Girls Roller Derby (1), Philly Roller
Girls from Philadelphia (2), Canadian Montréal Roller Derby (3),
Baltimore’s Charm City Roller Girls (4) and Steel City Derby Demons
from Pittsburgh (5), as well as four other US teams. But because the
second division doesn’t contain any European teams, LRG, in order
to be able to compete for a place in playoffs, needs to travel across
the Atlantic to play against D1- and D2-teams (as LRG did in June
2013), or get division 1 or 2 teams to visit Great Britain. The
pioneers always have to suffer. This also means that envious derby
sisters are left out in the cold as London Brawling doesn’t have
the time nor the desire to play “charitable” bouts against the
lower ranked teams.
Scoring
Points
are awarded to teams based on a formula that takes into account the
strength of the opponent, points scored and the “value” of the
bout i.e. is it a tournament bout or part of the ordinary season.
Tournament bouts are more valuable than ordinary bouts and for
example WFTDA playoffs and finals are ranked the highest. The total
number of points a team has is then divided by the total number of
bouts the team has played during the season. The formula encourages
teams to play against better-ranked opponents as teams’ ranking
scores are based on the total number of points in the bout. This
means that losing to a stronger team can lead to a better ranking
than beating many weaker teams by hundreds of points. The rankings
are publicized bimonthly. If a European WFTDA-team wants to advance
in the divisions and the ranking-list or overall is interested in
their rankings, the scoring (and due to that, also playing) becomes
challenging. For example our domestic WFTDA-team Helsinki Roller
Derby has, based on rankings published in April 2013, 80.68 points
having won one bout (Crime City) and lost twice (Stockholm, LRG) and
is thus ranked number 121. HRD is included in the third division and
what used to be its Eastern region. Each team receives a Strength
Factor based on their rankings and hence teams want to play both
higher ranked teams as well as teams in the division above. If HRD
for example wanted to climb in the WFTDA rankings, it should only
play against three teams in Europe: LRD (ranked 25), Stockholm Roller
Derby (ranked 103) and Bear City from Berlin (ranked 105), whereas
these teams wouldn’t have much incentive to play Helsinki as they
should seek out opponents ranked above them. Of course teams can play
against each other unofficially and this is exactly what happens in
the Finnish Cup as those bouts couldn’t in any case be WFTDA
sanctioned due to the non-WFTDA status of the leagues participating.
So it looks like the best way for lower-ranked teams to advance is to
inch along the rankings by playing WFTDA-member teams with similar
scores and taking part in any European tournaments, which would mean
getting the benefit of the tournament weight factor too. However,
playing the ranking game is not always so simple: Berlin, which is
generally considered to be the second best derby team in Europe after
LRG, is at the moment ranked as number 105.
Other
measurements
There
are of course other roller derby statistics in addition to the one
calculated by WFTDA. There’s the Derby News Network “Power
Rankings” which are updated monthly. In May 2013, that list is
headed up by 1. Gotham, 2. Oly, 3. Denver, 4. Texas ja 5. B.ay A.rea.
The same names can be found on the WFTDA list but in a slightly
different order. Every place, where derby is played, there are also
teams that are not affiliated with WFTDA – either due to their own
wishes or due to the external circumstances. These non-affiliated
teams can’t be found in the WFTDA rankings and, even though they
would be unlikely to change the pecking order at the very top, the
inclusion of these “dark horses” adds its own spice to the other
statistics in addition to the different formulas used to calculate
them. Let’s look at the Flattrackstats.com site for example, which
shows as the top five in Europe all the LRG teams, including also
home teams, with only Auld Reekie Rollergirls breaking the pattern.
Derbychart.com by Stat Man offers up a different option: 1. London
Rollergirls, 2. Stockholm Roller Derby, 3. Bear City Roller Derby, 4.
Crime City Rollers, 5. Tiger Bay Brawlers. Major Madness and Riff
Reff’s Euroderby.org has removed LRG’s A-team from the list and
the order of the top five changes a little also due to the different
calculation method: 1. Auld Reekie Roller Girls, 2. London Rockin
Rollers, 3. Tiger Bay Brawlers, 4. Stockholm Roller Derby, 5. Bear
City Roller Derby. Even the Finnish Cup has its own rankings, which
can be found at www.rollerderbyfinland.com. Its formula is in all its
simplicity as follows: a victory gives you two points and in the
event of ranking scores are tied, the determining factor will be who
won the bout played between the tied teams and only thereafter is the
score difference of that bout looked at. Simple is beautiful but only
as long as there are only six teams battling it out and not 6,000.
---------------------------------
Most
of the ranking providers are using formulas to predict the probable
results and winners of upcoming bouts or alternatively, the
probability of a win is tied to the divisions in which the teams
play. But below we cover only the basic of ranking the results of
bouts already played.
www.Euroderby.org (closed 2013)
- consists of the European teams
- the teams have been split into divisions based on last year’s performance
- the team from the higher division is expected to score 150% of the points against a team in a lower divisions
Example:
Helsinki Roller Derby A plays in division 1 and Kallio Rolling
Rainbow in division 2.
HRD
wins the bout 230 - 108. The points of both teams are multiplied by
Division Factor the thus resulting in relative scores.
HRD
= 230
KRR
= 108
HRD’s
division factor = 1
KRR’s
division factor = 2
HRD’s
relative score = Points x (Division 2 - Division 1) = 230 x (2 - 1) =
230
KRR’s
relative score = Points x ((Division 2 - Division 1) + 0,5) = 108 x
(2 - 1 + 0,5) = 162
HRD
wins and gets 3 points.
KRR
loses and gets 0 points.
Including
the Division Points
HRD
Div1 = 1
KRR
Div2 = 2
HRD
= Div1 - Div2 = 1-2 = -1
KRR
= Div2 - Div1 = 2-1 = 1
HRD
Ranking = 3 points + Division Points = 3 + (-1) = 2
KRR
Ranking = 0 points + Division Points = 0 + 1 = 1
If
this was the first bout of the season for both teams, the rankings in
Euroderby would for example for HRD look as follows:
Division
1 League: Helsinki Roller Derby
Team:
All Star Ninja Turtles
Bouts
played: 1
Points:
230
Score:
2
Rating
(score/bouts): 2
The
scores of the current number one team of the first division, Auld
Reekie, are 12, 219 and 2,4.
- includes all bouting European teams
- is based on a system where each team put into play half of their ranking points, which are based on the team’s previous bouts. The ranking points are then divided between the two teams in proportion with the points actually scored in the bout.
For
example, if Dirty River Roller Grrrls, currently ranked at 42 with
84.64 ranking points, were to play Lahti Roller Derby, which is
ranked 98 with 23.50 points, DRRG would put 42.32 points into play
and LRD 11.75 points. If the bout were to end with the surprise
result of 200 points to Turku and 250 points to Lahti, the ranking
point calculation for Turku would be as follows:
DRRG’s
points = 42,32/2 + (42,32 + 11,75)/2 x 200/(200 + 250) = 21,16 +
54,07/2 x 0,444 = 21,16 + 27,035 x 0,444 = 33,16
So
in the 24 May 2013 –rankings Turku would fall to number 83.
- includes all teams playing with the WFTDA and MRDA rules
- the algorithm is bases on the Elo system, which was originally developed for two-player games; the basic idea is that the players or the teams performance is a normally distributed random variable (in line with the Gaussian distribution). Even though the performance can vary greatly from one bout to another, the total picture of a team should on average follow the same pattern. For the single performance, the better formula would be the so-called logistic distribution. The power ratings, which define the team’s placement in the ranking table, are usually in the range between 500-1,000.
- The rankings are based the points differences of each bout, which rewards strongly offensive teams. This is why the Difference-overSum-formula is used as it evens out the rankings for teams that are more defensive. DoS-ratio 1 means a really clear victory and DoS -1 means a very clear loss. These are then compared to the expected results, which are counted with a separate formula.
DoS
= Team A – Team B
Team
A + Team B
For
example:
Kallio
Rolling Rainbow and Paris Roller Derby play each other and the bout
ends with Kallio winning 243 – 182. The formula would in that case
be: 243 – 182 / 243 + 182 = DoS = 0,14 (Paris DoS -0,08).
This
number is then compared with the ranking points as they were before
the bout whilst simultaneously comparing the estimated DoS with the
actual DoS number. One team will move up the ranking and the other
team will move down. The final power ranking between 500 and 1,000
will be arrived at by using the logistic distribution.
This
function also takes into account a small home court advantage (based
on research). Kallio’s previous points in the ranking were 644.4
(ranked 33) and Paris’ points were 669.7 (ranked 24). After the
bout, the ranking points are + and – 10.1 i.e. 654.5 to Kallio and
659.7 to Paris (the decimal rounding off will keep Paris at – 10).
The points would raise Kallio’s ranking to number 29 and would push
Paris down by one. The current number one of this ranking table is
London Rollergirls with 922.5 points.
- includes all the European teams and the rankings can also be reviewed for more limited areas: the Nordic region, Great Britain & Ireland and Western Europe
- is based on the score difference of each bouts, the points awarded for a win and a formula that rates a narrow lead higher than a score difference of 100 points
For
example, if Kallio Rolling Rainbow were to play Helsinki Roller Derby
and the result were to be 150 – 100, the points would be as
follows:
Points
percentage for KRR: points made / total points 150/250=60% i.e.
+0.600 points for KRR
Winning
percentage: 1 for a win, 0 for a loss, 100% i.e. +1.000 points for
KRR
Applied
percentage (unfortunately the formula is not very reader-friendly):
KRR 72,3% i.e. +0.723 points
To
determine the power relationships, Stat Man uses a value he has
empirically researched and which he calls the stot-value. The value
The
stot-value determines how difficult it is to beat a particular team
and it is calculated as follows:
All
the bouts played during the season:
25%
points
50%
wins
25%
applied percentage
A
team’s placement in the ranking is determined by multiplying the
applied score with the opponents stot-value i.e. the team’s
difficulty level. This number will be between 0 and 1 and to make it
more reader friendly it is multiplied by 1,000. For example, the
current number one London Rollergirls’ has a score of 234.3.
Originally published in KARU 1/2013
Text: Raisa Siivola
Translation: Schlagerlöf
Text: Raisa Siivola
Translation: Schlagerlöf
