I played a test of a real-life Capture the Flag game that used your phones for capturing the flag and others.

Your phone would contain a radar with your distance to the flag, and to catch other players you'd tap a tag button on the app.

It was fun, and I could see the potential. There is still plenty of issues with GPS tech but they were doing some fine-tuning using wifi towers / etc.

In this case, you only looked down at your phone to view radar, otherwise you ran as normal, and that's (mostly) safe. :)