This refers to a sprain of the big toe joint at the ball of the foot, it can occur if the joint is bent too far in either direction. It sounds quite trivial but can be a very uncomfortable experience and is best treated seriously.
You will have a notable injury and will experience pain on the top of the joint. Walking and running may be very painful initially. Rest, ice, compression and elevation are useful in the early stages.
Mr Willis-Owen will be able to check the foot and make sure there are no fractures or cartilage damage using X-rays. This injury usually settles on its own with time, but may take several weeks. Stiff soled shoes or even a surgical shoe is useful during this time.