A round-robin tournament or all-play-all tournament is a type of tournament in which each contestant meets all other contestants in turn. In a single round-robin schedule, each participant plays every other participant once. If each participant plays all others twice, this is frequently called a double round-robin.
In theory a round robin tournament is the fairest way to determine a champion among a known and fixed number of teams. Each team has an equal chance against all other participants. The element of luck is seen to be reduced as compared to a knockout system since a few bad performances need not cripple a competitor's chances of ultimate victory.
The primary disadvantage to a round robin tournament is the time needed to complete it. For instance, a 30 team tournament divided to three 10-team-groups would take 3*9=27 rounds.
Another con is that there is a high probability that many teams will end up in tied points after round robin. This situation can be handled with a tie-break game or so that the game between those teams that are tied will make the difference. However, also in this latter case there is a possibility that tiebreaks are needed because three or more teams can end up in the same points.
The possible tiebreaks might be a challenge time schedule wise.
Use of round robin
Round robin is used in major WCF tournaments so that the teams are first divided to 2-N groups and then round robin is played within each group. After round robin the best teams from each group advance to playoffs. The playoffs can be played with a normal cup format or with page playoff system.