What do u mean by knock …

In this type of tournament, the team which is defeated once’ gets eliminated immediately and will not be given another chance to play. The total number of matches to be played in this tournament will be equal to the number of teams participating minus one (AT—1),
E.g.,
if 21 teams are participating, the total number of matches will be 21-1=20. Number of teams in upper half.

Number of teams in lower half

Total number of byes
= Next power of two – total teams
= 32 – 21 = 11 byes

Knock-out Tournament Most of the tournaments are organised on the basis of knock-out. In this type of tournament, a team which is once defeated, automatically gets eliminated from the tournament. Only the winning teams continue in the tournament. It means that second opportunity is not given to the defeated team. Opportunities are given to the winning teams or players. For example, if four teams participate in knock-out tournament, the winning team is declared in the following way. In the 1st round, team A and B as well as team C and D play their matches. If team B and team D become the winners of 1st round, these teams, i.e., B and D get opportunity to play in the 2nd round and team A and team C will be eliminated from the tournament. Finally, the winner of match between team C and team D becomes the winner of the tournament.Read more on Sarthaks.com - https://www.sarthaks.com/12362/what-do-you-mean-by-knockout-tournament-draw-the-fixtures-of-21-teams-on-knockout-basis