Points Off Power Jams

Power jams in roller derby are a lot like turnovers in football. Both have a large impact on the outcome of a game. Both often trigger momentum shifts that can rally one team while leaving the other demoralized. Anyone who watches football can tell you that the announcers talk a lot about turnover differential and how it impacts the odds of winning. Turnovers make a big difference.

The same holds true for power jams in roller derby. If one team gets more power jams than their opponent, their chances of winning are obviously increased. Yes, there are a lot of mismatches in roller derby due to how young the sport is. Still, if 2 teams are similar in talent and skill, power jams can easily be the difference between victory and defeat.

One football stat that is often talked about alongside turnovers is "points off turnovers." Basically, it's the number of points a football team scores with the possessions immediately following turnovers. —The stat illustrates how much turnovers are effecting a game and how effectively a team is taking advantage of their opponent's mistakes. A team with 3 takeaways and 17 points off turnovers is really capitalizing on them. Conversely, a team that has 3 takeaways and only 3 points from them is wasting opportunities.

Enter "Points Off Power Jams" or PoPJ for short. Obviously, having a stat like this in roller derby could give you a lot of insight on how well a team is taking advantage of power jams and limiting the damage from them. Sounds great, right? Unfortunately, roller derby isn't as simple to break down as football. —Or maybe it's just that the sport of flat track roller derby hasn't been around long enough for people to really dissect it in this way.

The problem with tracking something like this is in differentiating which points resulted from the power jam and which points were just a result of normal play. You can't just look at the points or differential from full jams effected by jammer penalties. There are too many other factors in play. If a jammer gets double-slammed before going to the penalty box, 10 points from that jam are not a result of the power jam. Somewhere around 50% of jammer penalties also continue into the next jam. How do you take into account the new initial passes both jammers now need to complete before scoring?

Anyone can watch a bout and estimate a power jam's impact, but that's subjective. I hate stats that depend on interpretations because they're unreliable. What's needed is an objective set of rules to separate out the points scored as a result of the power jam from the points scored as a result of good pack play. Well, I've come up with a pretty good system that covers every scenario.

NOTE: For the sake of clarity and funness, let's call the jammer who is sent to the penalty box "Raskal Rae." The jammer who's scoring unopposed will be "Fannie Flash." Anyway, here are my rules for tracking PoPJ:


1. Jammer lap points are never counted. This is pretty straightforward. If Raskal Rae is lapped before going to the box, that point was not a result of the penalty. If she comes out of the box in front of Fannie Flash and is then passed, her point was the result of Fannie's blockers doing their job.
2. Jammer ghost points are always counted. Another easy one. As soon as Fannie Flash passes the first opposing blocker on a power jam, she gets the jammer point as well. Also, if Fannie is scoring but does not pass Raskal before she gets sent to the box, that 5th point is a result of the foul.
3. If Fannie Flash is between passes when Raskal Rae earns a penalty, PoPJ begins tracking immediately upon the foul being committed. This seems pretty simple, but it's important to spell it out this way. Technically, when a skater is sent to the penalty box, she is immediately off the track (and her ghost point is awarded if applicable). The time it takes Raskal to get to the penalty box is a direct result of the foul. Had the jam continued with her, we assume Raskal would have called it off to prevent any scoring from Fannie on her next pass. —And even if Raskal didn't have lead at the time or decided to let the jam continue, the points Raskal would have scored would have been offset by the points Fannie would have scored. The absence of Raskal scoring means a greater net gain for Fannie's team.
4. If Fannie Flash is in the middle of a scoring pass when Raskal Rae commits her foul, the points scored on that pass do NOT count towards the PoPJ (except for any jammer ghost point). Now we're getting technical. We are assuming that Fannie would have completed this scoring pass regardless of the penalty. Yes, this is a big assumption, but we need an objective way of tracking it. If you split apart scoring passes based on estimates, you start robbing the stat of its objectivity. The only option here is to not count the pass.
5. If Raskal Rae exits the penalty box on a scoring pass, PoPJ stops tracking points as soon as Raskal Rae enters the pack. Any points scored on a pass for Fannie Flash that is not COMPLETED prior to this are not counted (except for any jammer ghost point). The few seconds Fannie has to get out of the pack while Raskal is approaching are definitely a result of the foul. However, if both jammers end up in the pack at the same time, we view them as on parallel scoring passes. Because Raskal Rae's scoring pass is obviously post-penalty, we should view Fannie's pass the same way. Fannie Flash does have the option to call off the jam before Raskal gets to the pack, in which case the points from the unfinished pass should still be counted (because in that case Raskal never began a scoring pass). If Fannie fails to call off the jam before Raskal scores, we view it as a tactical decision. If Fannie did not have lead, that is the result of a error on Fannie's part (or her team's). Either way, if the scoring passes become parallel, we do not view the points scored as earned towards PoPJ.
6. If Raskal Rae exits the penalty box needing to complete an initial pass, PoPJ continues to track points scored by Fannie Flash, but only for the current / next pass (except for any jammer lap point). Fannie does not want to call off the jam right away because she's still scoring unopposed. She has 1 pass to give before Raskal scores, so we are giving her 1 pass to finish her scoring. This holds true even if Raskal completes an initial pass and begins scoring before Fannie completes this pass. Raskal's initial pass was parallel to the current/next pass for Fannie, so Fannie's pass still counts even if she is later lapped by Raskal while still in the middle of it (because Raskal's scoring pass is not parallel to it). If Fannie fails to call off the jam before Raskal scores, we view it as a tactical decision or an error by not getting lead (same as in #5).


The important thing to remember in all of this is that a scoring pass is either counted or it isn't. Again, the reason for this is to eliminate guesswork and build the stat around objective, factual data.

No stat is perfect. In reality, all power jam scoring passes are partially helped by the penalty and partially helped by the pack play. Hell, roller derby as a whole is a combination of any number of different variables at any given moment. It's like "butterfly effect" the sport. —But that's why I like experimenting with stats for it. There are so many possibilities when it comes to measuring how one thing effects another. I geek out about it. A stat like this is simply a slice of the sport that can help you look at a bout in a new way and maybe gain additional understanding.