Roller derby is played on a flat, oval shaped track. The dimensions and shape of the track are the result of flattening a roller derby banked track. So, it is not a perfect oval, as the outside track corners are offset slightly. This track is 88 feet long and approximately 53 feet wide, and roughly 180 feet in circumference (148.5 feet on the inside and 236.5 feet on the outside). The use of a flat track allows derby to be played in a wide variety of venues, and spares the massive expense of acquiring, building, storing, and maintaining a wooden banked track.
Derby skaters all skate on quad roller skates - not rollerblades. Roller derby is a full contact sport—all skaters wear a full complement of of safety equipment: helmet, mouth guard, elbow pads, wrist guards, and kneepads. This safety equipment is required and is worn to minimize the chance of injury. For their safety, refs are also required to wear the same safety equipment as the skaters, with the exception of the mouth guard (since they need to yell out penalties and blow whistles).
A bout consists of two periods of 30 minutes each, though intra-league play is often played with shorter, 20-minute periods. Generally, there is a halftime between the periods. Often, bouts are staged as doubleheaders, with two bouts in a night. These can be played either with both periods of one bout being played consecutively, or by staggering the first periods of the first and second bout, followed by the second periods of the first and second bout.
The second period is a continuation of the first period - all the points and penalties are carried over from the first to second. If a skater is in the penalty box when the first period ends, she starts the second period in the penalty box.
Bouts are broken into jams of up to two minutes each, with 30 seconds between jams. The period clock continues to count down during this entire time (unless either team or the officials call a time out). Jams can also be called off early by a skater who has earned the strategic advantage called Lead Jammer status.
Each jam has up to five skaters from each team skating at a time (some skaters may be penalized and sitting in the penalty box). One skater from each team (the Jammer) has the ability to score points by passing opposing skaters. The opposing skaters, of course, will do their best to prevent this.
After the first whistle blows to start the jam, everyone except for the jammers may start skating forward. This is sometimes done quickly, other times more slowly (for a variety of strategic reasons). Once those skaters (the pack) have cleared the starting line (called the Pivot line), a second (double) whistle is blown and the jammers are released. The first Jammer who makes her way through the pack, having both cleared the front-most pack skater and having passed all opposing skaters legally and while skating in bounds, is declared the Lead Jammer.
Sometimes a skater is the first to get through the pack, but she may not be Lead Jammer due to not having passed all opposing skaters legally and in bounds—being first doesn't matter if not done correctly!
After her initial pass, the Jammer will earn one point for each opposing skater she passes legally and in bounds on subsequent passes (normally up to four points per pass). During her pass, she will also earn points for opposing skaters who are in the penalty box. Points for players in the penalty box are awarded to the Jammer as soon as she passes one opposing player in the pack. If the opposing Jammer is in the box (a power jam situation), or if she laps the opposing Jammer, she can earn five points per pass.
If the opposing Jammer is in the penalty box, it is not uncommon for the Jammer to score ten points or more—even 30 points is not unheard of in a power jam. As a result, the balance of a game can quickly shift when a Jammer is in the box.
Stopping the Jam
A jam ends when the two-minute jam clock expires, or the Jammer with Lead Jammer status calls it off by touching both her hands quickly to both her hips. If neither Jammer has Lead Jammer status (which can happen if the Lead Jammer goes to the box for a penalty), the jam will continue for the full two minutes.
Strategically, a Lead Jammer uses her status to maximize the number of points she can score while minimizing the number scored by her opponent. Often, the Lead Jammer will call off the jam just before the opposing Jammer has a chance to score any points, but she may also choose to run out the clock if her team is ahead, or push her luck and try to get in an extra couple of points or even entire passes, in hopes that her Blockers can contain the other Jammer long enough for their team to score more points.
Note: When the period clock expires during a jam, that jam will continue until the two-minute jam clock expires or until the jam is otherwise called off.