Original: These are common in those sports and games where each match must involve a small number of competitors: often precisely two, as in most team sports, racket sports and combat sports, many card games and board games, and many forms of competitive debating.
Simplified: These are common in sports and games where each match can only have a small number of competitors, often  two, as in most team sports, racket sports, combat sports, many card games and board games, and competitive debating.