A subgroup of a group can also be defined as another abstract group along with an injective homomorphism (or embedding) from that abstract group to the given group. Here, the other abstract group can be naturally identified via its image under the homomorphism, which is the subgroup in a more literal sense.
For the skate brand of the same name, see Roller Derby (brand). Roller derby is a contact sport played by two teams of five members roller skating in the same direction around a track. Game play consists of a series of short match ups (jams) in which both teams designate a jammer who scores points by lapping members of the opposing team.
Gaffers tape, the tape that so many flat track roller derby teams use for track layout, is made from two of the most volatile raw materials used in manufacturing. The cloth is woven from cotton, a commodity that is subject to price vagaries caused by the weather and constantly increasing internataional demand.