Page "Single-elimination tournament" Paragraph 9

In cases where the number of competitive entities at the start of the tournament is not a power of two, some competitors may receive a bye in the first round, which entitles these competitors to advance to the second round automatically without playing.

Often, these byes will be awarded to the highest-rated competitors in the event as a reward for some previous accomplishment ; indeed, in some American team sports — most notably American football — the number of teams qualifying for the postseason tournament will be intentionally set at a number which is not a power of two, in order to provide such an advantage to a high-achieving team in the just-completed regular season.

Additionally, the player / team getting byes may get them exclusively by luck or random chance ( i. e. if there are 7 competitors, one random one will automatically advance to the next round )