Jam Expectancy Study: Power Jams

photography by Fotodog

In both the introduction and situations posts, we’ve talked about expectancy on a jam-by-jam basis.  We’ve counted one absent blocker at the double whistle as a -1 toward the iPS.  It’s a decent way of measuring the cost of blocker penalties because the beginning of the jam is when pack strength matters the most.

Jammer penalties, on the other hand, are a completely different beast.  Whenever a jammer is in the penalty box, it’s a very big deal.  The situation in the pack is secondary to the lack of a jammer, so we need a different approach for measuring the effect of power jams.  We need something that tracks over multiple jams and directly addresses the points scored as a result of the power jam.  To this end, I created a stat called Points Off Power Jams, or PoPJ for short.

The goal was to separate out the points scored as a result of the power jam from the points scored as a result of normal pack play.  Anyone can watch a bout and estimate the number of points resulting from a power jam, but I wanted an objective way of tracking it.  There are a lot of different scenarios that can come into play surrounding when a jammer enters or exits the penalty box, so I created a set of rules to address exactly when PoPJ starts and stops counting points:

(1) Jammer lap points are never counted.
(2) Jammer ghost points are always counted.
(3) If the power jammer is between passes when the boxed jammer commits the foul, PoPJ begins tracking immediately.
(4) If the power jammer is in the middle of a pass when the boxed jammer commits the foul, any points scored on the current pass are not tracked towards PoPJ (except for any jammer ghost point), and PoPJ begins tracking as of the next pass.
(5) If the boxed jammer exits the penalty box having already completed an initial pass and eligible to score points, PoPJ stops tracking points as soon as the boxed jammer enters the pack. Any scoring pass not COMPLETED prior to this is not counted (except for any jammer ghost point).

(6) If the boxed jammer exits the penalty box needing to complete an initial pass to become eligible to score, PoPJ continues to track points scored by the power jammer, but only for the current / next scoring pass (except for any jammer lap point).
If you’d like a more detailed explanation of the rationale behind this system, you can read my personal blog post about it here.

Using these rules, I tracked the PoPJ for every jammer penalty in the 20-bout study.  The goal was to measure the average impact of a 1-minute power jam.  It’s important to note, though, that a significant number of power jams are less than a minute.  The power jammer is sometimes also sent to the box, resulting in both teams having shortened power jams.  Occasionally the bout also ends prior to a jammer being released from the box.  I decided to calculate averages both with and without shortened power jams.  Here are the results:

Samples Total PoPJ Avg PoPJ
Full 1-Minute Power Jams 151 1843 12.21
All Power Jams 188 1984 10.55

Avg Power Jams Per Team Per Bout = 4.7

Honestly, I’m surprised by how low this is.  I went into this expecting the average to be 15+ points.  After all, the top teams in WFTDA are generally really good and capitalizing on jammer penalties.  When you hear the words “power jam,” you immediately picture a handful of grand slams and a 20-point swing.  The truth is that these teams are as good at killing a power jam as they are at taking advantage of one.  There were definitely a decent number of 19-point gougers, but there were also a lot of 5-point kills.  Some power jams even resulted in zero points.

It’s worth pointing out that the average total PoPJ for a bout is almost exactly 50 points (it’s 49.60).  If a team can manage to skate an entire bout without losing their jammer, they can theoretically expect to gain a 50-point advantage as a result.  Of course, skating an entire 60-minute bout without sending a jammer to the penalty box is nearly impossible.  Every team included in this study gave up at least 2 power jams in every bout.  Still, limiting your own jammer penalties can really help.  At the end of the bout, you want to make sure your total PoPJ is greater than you’re opponent’s.  If you can drive down the number of power jam points you’re giving up, you can make it really difficult for your opponents to outscore you.

The total PoPJ for any team is effected by both the number of power jams a team gets and how well that team capitalizes on them.  By the same token, the opposition’s PoPJ is effected by the team’s propensity for committing jammer penalties as well as their ability to limit the damage from them.  I started thinking about how power jams effect teams differently, and I decided to run the numbers for all 12 teams across the 20-bout study.  Let’s take a look at how they did in these categories:

Team Bouts Avg Power Jams For Avg PoPJ For Avg Total PoPJ For Avg Power Jams Allowed Avg PoPJ Allowed Avg Total PoPJ Allowed
Charm City 2 3.5 13.71 48.00 4.5 14.22 64.00
Gotham 4 6.0 14.17 85.00 4.0 11.25 45.00
Kansas City 5 4.6 9.30 42.80 4.0 9.05 36.20
Minnesota 3 5.7 10.59 60.00 3.0 11.56 34.67
Naptown 2 5.0 7.90 39.50 4.0 10.63 42.50
Nashville 2 5.0 5.40 27.00 7.0 13.14 92.00
Oly 5 5.6 9.64 54.00 4.6 9.26 42.60
Philly 4 3.3 9.69 31.50 4.0 13.69 54.75
Rocky Mountain 3 5.0 12.73 63.67 8.0 9.63 77.00
Rose City 2 5.0 10.50 52.50 5.5 11.73 64.50
Texas 5 4.0 11.20 44.80 3.8 9.79 37.20
Windy City 3 3.7 9.55 35.00 6.3 7.58 48.00


There’s a lot of analysis that can be done here regarding the teams’ different styles of play.  I’ll let you draw your own conclusions, but I’d like to point out that there are several factors that determine how a team performs with and against power jams.  How quickly does a team recognize and react to jammer penalties?  Which opponents did a team face in these bouts?  Teams have a certain amount of control over how often they send their own jammer to the penalty box, how well they take advantage of power jams, and how well they kill a penalty.  The most difficult thing for a team to control is how often the opponent gives them a power jam opportunity (although good teams can force more jammer penalties).

What I take away from all this is that the cliche is true: Power jams matter a lot.  —Though maybe not for the same reasons as is widely thought.  Yes, one power jam can be a big deal, but on average it’s not that much of a crisis.  The big thing is the cumulative effect of power jams.

In the next and final article of the series, we’ll take a look at the value of getting lead jammer.  Just how important is it?  We’ll also be examining strategy and the effectiveness of poodling.   See you then.


P.S. –  I added this data in the comments section of the last article, but as we were just comparing different teams’ performances as it relates to power jams, I figure it’s interesting enough to add on to the end of this article as well.  The only new stat here is iPA, which is Initial Pack Advantage (own iPS – opponent’s iPS).  I calculated the total iPA for each team in the study so you can get an idea of how often the teams had the pack advantage or were outnumbered.  Take a look:

Team Bouts Jams Total iPA
Charm City 2 94 -31
Gotham 4 169 +5
Kansas City 5 213 +35
Minnesota 3 136 +36
Naptown 2 80 -15
Nashville 2 77 -3
Oly 5 211 -5
Philly 4 169 +9
Rocky Mountain 3 115 -7
Rose City 2 85 -23
Texas 5 222 +20
Windy City 3 123 -21

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