tennis coach – specific need – record only prior X seconds after button push

As mentioned above – I am a tennis coach. I am looking for an easy way to create clips of specific video segments from a coaching/training session.

The wish is that I can be on court feeding, or watching players play (with video camera already in place and recording), and press a button either on phone or remote which via Bluetooth or Wifi alerts the recording camera to retain the video from the last X number of seconds (maybe 5 or 7).

At the end of the session, all other video from that session that was not just prior to when I pushed the button is deleted, and you’re left with however many short clips.

The challenge I have as a coach who likes using video is that it takes a long time to actually edit and sort stuff, and most of the video is filler and not really the focus of what I would like to discuss with students. This ability would allow me to use video almost daily, VS only at camps and tournaments other setups where we have more time and manpower to go through things.

Any ideas on either software or hardware that could create this situation? I do have a go pro hero3+, and obviously a smartphone.

Thanks!