If you have a custom clip that starts on the very first frame of the track, OnBehaviourPlay is not called. This is only if you're in edit mode and hit play on the timeline (not the game itself). (this is on a custom PlayableBehaviour created using the playables wizard) This is really annoying because you can't rely on using OnBehviourPlay in edit mode, and we must do alot of our animation in edit mode. OnBehaviourPlay is not called on Sprite OnBehaviourPlay is called on Sprite