https://www.championdata.com/faqs/afl/
Missed Tackle (Broken Tackle)
Q: The player clearly made physical contact with the opponent but no tackle was awarded. Why?
A: If a player is being impeded by an opponent and then breaks the attempted tackle to get a disposal away, then no tackle will be awarded.
No Tackle
Q: A player was tackled as they disposed of the ball. Why wasn’t a tackle awarded?
A: If a player attempts to tackle a player in the act of disposing of the ball, and that disposal is deemed to be effective, then no tackle will be awarded. If it leads to an ineffective disposal or a clanger disposal, or prevent a disposal, then a tackle shall be awarded. The defensive player is credited with a tackle attempt.