Some details on the setting:
The bears emerged from their caves in 1962. For seven years, a united mankind fought a long, brutal war against their common foe, only to be defeated by the superior technology of bears, in the form of their mighty chrome bear suits. For 26 years, technology has advanced rapidly, and the bears created roller derby as an oulet for humanity. The roller derby tournements are serious business, as the losers are selected as the nex targets for population control.
The rules of roller derby are simple. Two teams of five start back to back, and then race to skate three laps through an obstacle filled death course. Any methods short of mega class weapons, magic, and psionics may be used to impede the progress of the other team. Teams judged to be cheating during a match have their skates destroyed by explosives. Then, they are disqualified. Aside from losing a match, there is no penalty for cheating, and cheating is rampant. All derbyists in a normal roller derby are supposed to be humans, with medical cybernetics only.
In addition to typical roller derbies, the Roller Bear circut also includes mega derbies, where the teams are equipped with mega class weapons and armor, and ride on rocket powered motorcycle skates. Mega weapons and armor have a power level equivelent to modern main battle tanks, and are quite frighteningly powerful. Magic and psionics are allowed in mega derbies, but intentionally killing an opponent is grounds for disqualification. (Mega armor is strong enough that it usually gets immobilized and totalled before the occupants are killed)
In Roller Derby, the most infamous and pervasive type of cheating is the juicer; basically an example of performance enhancing drugs gone amok. Juicers feel no pain, and no fear. Along with the blood clotting drugs, painkillers, and adrenal supplements they're on, Juicers are almost impervious to conventional weapons. Though a team that obviously has a juicer on it will be disqualified, nearly every team has at least one juicer. The most common way of dealing with juicers is to carry low end mega weapons into the roller derby, and quietly use them on those tagged as juicers.
Summoning of demons and use of illegal magic is also quite common. Although cybernetics are technically restricted to "medically neccesary" components, there are no required medical exams, and performance is the only real measure used to determine the qualifications of the team. Accusations of cheating are usually considered by the judges to be hypocritical and cowardly, and quite often evidence of cheating. Fundamentally, Roller Derby is all about entertaining the judges, and cheating even more than your opponent without getting caught.