Challenges are the quickest way to gain BP and move up through the Battleranks and Classes.
Challenges follow a few rules.
Each student may only participate in a challenge (either as a challenger or defender) 1 time per school day. Matches on the seventh day of each week are prohibited as it is considered a rest day for all students. Matches outside of school grounds are also prohibited.
Wager Matches are the most common type of match and may be refused freely. A wager match is when two students place a bet with BP (and sometimes other things) on the outcome of their match. The winner takes all. During a Wager Match one can invoke an "Ante-Up" to ignore the usual challenge limit rules to immediately re-challenge a victorious foe. A new wager is placed when this occurs and the winner (whoever that might be) takes all of the wagered BP from both matches. An Ante-Up challenge can be freely ignored, however.
Class Challenges are when a Ranked student from one class challenges for a position in the next highest class above theirs. In a Class Challenge, the higher Class student being challenged CANNOT be a Ranker within that class. They may refuse the match by paying all of their current BP as a penalty but if they have no BP to pay they must accept the Class Challenge. If the lower Class challenger wins the match, they swap places with the loser – moving up a Class as the loser drops a Class. Both participants BP totals are also reset to 0. It should be noted that Class S students are never allowed to refuse a Class Challenge.