Overwatch's new Capture Highlight feature allows you to press F9 to save your last 12 seconds of gameplay, or the active Play of the Game. After the game, you can go to your Highlights to replay what you saved or export it as a video file.
However, this feature is not available at all times. For example, if you try to use it in the Practice Range you'll see the error message "Highlights unavailable". I was also unpleasantly surprised when, after making an exciting play in a No Limits arcade game, I pressed F9 and nothing happened, not even an error message. It also doesn't seem to be supported in pre-game skirmishes.
When am I able to use the Capture Highlight feature? Is it only in particular game modes? In modes where it is supported, is it available through the entire game, or is it disabled at times the clock isn't running, such as the set-up phase and the few playable seconds after a round? What about during the Kill Cam, or Death Spectating? What if you're spectating a match instead of playing it?