The undercard, or preliminary matches (sometimes preliminary card), consists of preliminary bouts that occur before the headline or "main event" of a particular boxing, professional wrestling, horse racing, auto racing, or other sports event. (In auto racing, however, the term "support race" occurs more commonly.) Typically, promoters intend the undercard to provide fans with an opportunity to see up-and-coming fighters or fighters not so well known and popular as their counterparts in the main event. The undercard also ensures that if the main event ends quickly fans will still feel that they received sufficient value for the price of their admission.
In auto racing, support races occur not just before the feature race, they occur on qualifying day where attendances are typically low and after the completion of the feature race, purposely to lessen the effect of traffic congestion outside venues common in major championship rounds, as spectators make their way home. Examples of notable support races include Porsche Supercup and GP2 Series, both supporting the Formula One World Championships, although the latter is considered to be a feeder series (for young drivers who desire to make the final step to Formula One). The Indy Lights series supports the IndyCar Series, and the NASCAR Xfinity Series and Camping World Truck Series effectively support the top-tier Monster Energy NASCAR Cup Series. In some series (most notably on oval tracks), the support races take place on both practice and qualifying days, and there is no support race on the day of the feature. A notable example is NASCAR's Monster Energy Cup Series, where all support races are held on days leading to the feature, although it can be run on feature day if inclement weather forces such.
In boxing, undercard matches usually last between four and eight rounds, depending on the experience of the boxers in those matches (entry-level boxers, often making professional debuts, have four rounds, while boxers at the intermediate level are given between six and eight rounds), with some undercards on major championship cards being ten rounds if the boxer is at the advanced level but not participating in a championship match. If an undercard match is a championship match (less popular weight class or regional championship), the undercard match is also twelve rounds, owing to regulations. In professional wrestling, undercard matches usually last for five to ten minutes: the audience does not have to wait too long for the main event and the promoters often have to fulfill contractual television agreements. Professional wrestling unofficially subdivides the undercard into uppercard, midcard and lower card matches, which roughly correlate to the fame and quality of performance of the wrestlers involved.
The opening act is a similar concept in non-sports entertainment.
A main event usually takes place as the final match of a title-match-system sporting event. The term occurs primarily with reference to combat sports such as boxing, professional wrestling and mixed martial arts. The main event, generally the most prestigious match on the card, has the most promotion behind it. The match commonly involves a contest for a top championship, but may feature another special attraction.
The headliner is a similar concept in non-sports entertainment.
Multiple main events
Sometimes, multiple matches of equally high importance take place on a card, occasionally at intervals throughout (to sustain spectator interest for its duration), but generally at the end in succession. This can be billed as a "double main event" or "double-header" or (rarely) as a "triple main event" or "triple-header". Advertising for sporting bouts focuses primarily on their main events.