I think I've posted this before, but most GPS watches really struggle with refereeing due to the "polling interval". The majority check your position every 5 seconds, and for most activities they can then guestimate your path as you are moving in a straight line. That doesn't work for refereeing as you obviously change direction a lot and it totally confuses the watch.
The Polar v800 by default is every 5 seconds, but it has an option of changing to every second, with the proviso that this will drain the battery much faster. I enabled that when I changed from a Garmin Forerunner to it, and it really was a game changer in the distances I thought I was covering, down by as much as a third. To check it wasn't my body that was broken I switched back to the Garmin and the distances went right back up again, as did they when I set the v800 back to the default polling setting. Bottom line is that distances covered when refereeing are a very rough guess when using anything but the very top end GPS watches.