While watching the video above, keep a close eye on the man and his son crossing the road in the right-hand corner of the screen.
In the footage, filmed using a helmet-cam by a motorbike rider in London and uploaded to YouTube by László Csőke, we see the man suddenly noticing something down a side road. As another man in a hood races around the corner clutching a hoverboard, the first man lunges forwards and trips him to the ground, before chasing after him and scaring him away from the dropped hoverboard.