The term "kickoff" has several meanings, depending on the context in which it is used.
1) In American football, a kickoff occurs at the beginning of each half and after every score when the ball is placed at the 20-yard line for the receiving team to start play.
2) In association football (soccer), a kickoff also takes place at the start of each half and after every goal is scored, with one team passing the ball to their opponents to begin play.
3) In other sports such as rugby or Australian rules football, a kickoff occurs when the game starts or after a score, where the opposing teams take turns in attempting to kick the ball between two goalposts.