This is a total non story just like the tv reports of officers playing hide and seek in police cars on nights or cricket in the cell area. There job often entails a lot of waiting for events to happen why should they not amuse them selves and stay fit and alert in the dull bits .
Give me a reason and i'll slag off the police till i'm blue in the face but having some harmless fun and a laugh during your working day is not an issue at all.
I assume they were a van crew and the shields were in the van anyway if they had booked the shields out to go sledging that would be a tad odd and i'd love to see the paper trail.