The Rules of Flat Track Roller Derby

2.4 - Jams

2.4.1 - A period is divided into multiple jams. There is no limit to the number of jams allowed in each period.

2.4.2 - A jam may last up to two minutes. Jams begin at the jam-starting whistle and end on the fourth whistle of the jam-ending signal (see Section 2.9 - Whistles).

2.4.3 - There are 30 seconds between jams.

2.4.4 - If all skaters are not on the track at the jam-starting whistle, the jam will start without the missing skater(s). If skaters are not in position at the jam-starting whistle, they will be subject to false start penalties (see Section 6.13.1 and Section 6.13.22).

2.4.4.1 - Jammers are considered in position and ready if they are entirely in bounds when the jam-starting whistle is blown. Jammers are subject to false start penalties if they are not on or behind the Jammer start line at the jam-starting whistle (see Section 6.13.22 for specific penalty details). Jammers are permitted to put on their helmet covers after the jam has started. However, each Jammer must have their helmet cover on their head or in hand before the jam-starting whistle. A helmet cover cannot enter a jam in progress.

2.4.4.1.1 - If the Jammer is not on the track and entirely in bounds when the jam-starting whistle is blown, the Jammer will not be permitted to join the jam in progress. No penalty will be issued.

2.4.4.2 - Pivots and Blockers are considered in position and ready if they are entirely in bounds by the jam-starting whistle (see Section 6.13.6). They are subject to false start penalties if they are not in position (see Section 6.13.1 and Section 6.13.22). Pivots are permitted to put on their helmet covers after the jam has started if they have the helmet cover in their hand at the jam-starting whistle. A helmet cover cannot enter a jam in progress.

2.4.4.2.1 - If a Pivot or Blocker is not on the track when the jam-starting whistle blows, that skater will not be permitted to join the jam in progress. No penalty will be issued.

2.4.5 - The jam is over when an official calls it off with four short whistle blasts. The jam ends on the fourth whistle, whether or not the whistles were inadvertent or incorrect.