The Jammer Quotient Explained

Defecaitlin takes the lead


Since I began to watch roller derby, I’d always wondered where the stats were. From what I could tell the leagues made a huge effort to record data—all those people sitting in the centre of the track and around the penalty box pens in hands—but as a fan I wasn’t seeing them. And since roller derby is a relatively new sport (particularly in its flat track form), and I new to it, I didn’t even know which stats were important and worth following. The Derby Nerd went to work.

Every major sports league finds some way to statistically compare its players, and I wanted some way to do the same with roller derby. The JQ is the best way I could think of to compare jammers, who have the most visible role on the track.* The JQ is a statistical comparison of jammers based on their rankings in five categories. Here are the the JQ Ratings for the February 27th,2010,CN Power (199) and Rideau Valley Vixens (49) bout at The Hangar.

Jammer Total Points Points Per Jam Plus/ Minus Jam % Lead % JQ
Lunchbox (CNP) 48 (9) 4.36 (9) +36 (9) 23.4 (8) 72.7 (9) 44
Land Shark CNP) 53 (10) 3.78 (7) +45 (10) 29.7 (9) 57.1 (7) 43
Defecaitlin (CNP) 45 (8) 4.5 (10) +29 (8) 21.2 (6) 70 (8) 40
Marvel S. Maven (CNP) 25 (7) 4.16 (8) +20 (7) 12.7 (3) 100 (10) 35
Soul Rekker (RVV) 19 (6) 1.18 (4) -35 (5) 34 (10) 50 (6) 31

Below is a breakdown of the five categories used to determine the total JQ  (only the top five in each category are shown). For a condensed explanation, check here.

Total Points

Jammer Total Points
Land Shark (CNP) 53 (10)
Lunchbox (CNP) 48 (9)
Defecaitlin (CNP) 45 (8)
Marvel S. Maven (CNP) 25 (7)
Soul Rekker (RVV) 19 (6)

When all is said and done, most points always wins. There’s no way any analysis of jammers could exclude this. Land Shark was the workhorse for CN Power putting up a remarkable 53 points.

Points Per Jam

Jammer Points Per Jam
Defecaitlin (CNP) 4.5 (10)
Lunchbox (CNP) 4.36 (9)
Marvel S. Maven (CNP) 4.16 (8)
Land Shark (CNP) 3.78 (7)
Sister Disaster (RVV) 1.57 (6)

Points per jam is also an important indicator of a jammer’s value, particularly in situations where a team might need a guaranteed score, or if the opposing team’s jammer is in the penalty box and a team wants to be sure to put up a lot of points. Defecaitlin may not have been as busy as Lunch Box or Land Shark (jamming anyway; she did her share of mixing it up in the pack too), but she made the most of her jams, gaining well over a full score (4 points) each jam.


Jammer Plus/ Minus
Land Shark (CNP) +45 (10)
Lunchbox (CNP) +36 (9)
Defecaitlin (CNP) +29 (8)
Marvel S. Maven (CNP) +20 (7)
Ripper A Part (RVV) -25 (6)

The last of the pure points categories is the plus/minus. A jammer’s plus/minus indicates the difference between the amount of points a jammer scores and the amount of points the opposing jammer scores against her. This is a good indicator of how well aware a jammer is of the other players on the track at all times. Land Shark (and the other CN Power jammers) dominated in this category as well.

Jam Percentage

Jammer Jam %
Soul Rekker (RVV) 34 (10)
Land Shark (CNP) 29.7 (9)
Lunchbox (CNP) 23.4 (8)
Ripper A Part (RVV) 23.4 (8)
Defecaitlin (CNP) 21.2 (6)

The jam percentage represents the percentage of a team’s jams that a jammer does. This is the only category that has two members of the Vixens in the top 5. Soul Rekker really stepped up for the overmatched Vixens and wore the panty every third jam for both halves, a truly remarkable performance.

Lead Percentage

Jammer Lead %
Marvel S. Maven (CNP) 100 (10)
Lunchbox (CNP) 72.7 (9)
Defecaitlin (CNP) 70 (8)
Land Shark (CNP) 57.1 (7)
Soul Rekker (RVV) 50 (6)

The final category, the lead percentage, represents the percentage of a jammer’s jams in which she wins lead jammer. Marvel S. Maven made the most out of all the jams she got, never giving up the star on any of them. It’s interesting to note that Land Shark and Soul Rekker, who did the most jamming for each of their teams, and often against each other, had lower jam percentages. I suspect that patterns such as this (and the match ups they represent) will be most evident in the final two categories.

I’m looking forward to applying the JQ over ToRD’s full 2010 season.

Just a note: There’s a ToRD “Fan’s Choice” scrimmage this weekend that should be a lot of fun. The first fans who arrive get to choose which players are on which team. Word around the track is that there will be guests from other leagues including some fan favourites from Forest City.

(*A similar comparison could be done with blocker stats too, and I’ll start working on that soon).


  1. Interesting stuff. Scoring stats in derby seem to me to present a lot of strangeness because getting a +2 in one jam could actually be a whole lot more of an accomplishment (2 equally skilled jammers) than a +10 jam (one jammer in the box). It’d be intresting to see some sort of way to do split stats based on the quality of the opposing jammer once there’s enough data. Stuff like PPJ vs jammers who have a avg PPJ > 4.

    Defecaitlin, who I can only assume is fresh meat since I don’t remember ever having seen her before, is on the short track to ROY based on her performance vs RVV. At the half, she’d made it clear that she’s as good a skater as any of the other top ToRD jammers. I can’t wait to see what she can do once the season rolls around.

    Something else I wonder if you can quantify is the inopportune penalties. There were a couple of games last year where Dolly Destructo took bad penalties (in my eyes anyway) while jamming that nearly (or did) blow big leads. I think one of them was a CN Power game last year, and the other was either a semi final or final.

  2. Very interesting comments! Definitely room for refinement. I’ve been wrapping my head around this for a long time, and this certainly wasn’t the first system I came up with…just the most balanced.

    Defecaitlin is better known as Dust Bunny (from the Gore Gore Roller Girls), ToRD’s 2009 Jammer of the Year.

    Very accurate assessment of Dolly Destructo’s penalty woes (BTW she led ToRD in penalty minutes last season). If you’re talking about what I think you’re talking about, you are referring to the Chicks Ahoy bout against the Death Track Dolls. In the final five minutes she took some inopportune penalties as jammer that allowed the Dolls to make up (nearly) 30 points over the final few jams.

    In this system, points against (in plus/minus) count even if the jammer is in the penalty box (and if a jammer is in the box at the beginning of the jam, this also counts against her Lead %).

  3. This is great stuff. I have always thought that stats are being under-utilized even by the biggest derby nerds, and that we are just beginning to scratch the surface of their utility now with stuff like this. Awesome!

    I think an interesting component to consider adding would be quality of the packs (both for and against). This could be expressed simply as ratio of opposing to to friendly pack players starting the jam. For example, if the jam starts with 2 teammates in the box, but all 4 on the track for the opponent, and the jammer gets 10 points regardless- well that is more impressive than the opposite. In that case the jammer is facing a 1:2 disadvantage, so that jam would get weighed slightly more than a jam where the pack ratio was 1:1 or 4:3 or whatever.

    just something to think about- I look forward to reading future posts!

    Caesar- Ohio Roller Girls

  4. That was definitely one of the bouts. It made for an exciting finish, but all i could do was shake my head at the penalties. After I wrote that comment I went back and read your other posts, which pointed out the Defecaitlin == Dust Bunny stuff, so thanks for clearing that up.

    I also can’t believe you rewatched all the video to get the numbers. That’s dedication. I wonder if there’s an easy way that ToRD could make stats numbers public, have you talked to them about it? It’d be cool to see that stuff online and easily exportable / manipulatable.

  5. Agreed – I would like to see ToRD publish their stats to make the more readily accessibile to the public. It would raise the credibility of the sport and would encourage another level of public involvement. Plus, if more metrics could be developed, there could be statistical evidence to back up jammer selection, pack make-up and etc. to assist teams in developing plays for each game. The could help raise the quality of play for all teams and possibly give some struggling teams (or new ones, should they spring up) greater odds for success.

    I would also be interested in further developing the Quotient by weighting some of the components (Total Points, Points Per Jam, Plus/Minus, Jam Percentage, Lead Percentage) and developing a comprehensive stat for the player across multiple games and opponents.

    BTW: are you going to develop a Facebook presence? Please? RSS your posts to a Facebook page!

  6. That’s the plan, Lauren! I developed this stat to apply to ToRD’s 2010 regular season; I think that will be its true test.

    And I will develop a Facebook presence by the start of the season (May).

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