If a runner falls when running in front of the bulls, the best thing to do is to cover your head with your hands and remain lying still on the ground until all the animals have passed. Other runners will soon let you know when it is safe to get up. It is better to suffer some possible bruising from the hooves than to run the risk of being gored if you get up just as they bulls are passing. Besides, the natural instinct of the pack is to try to go over any obstacles that are in their way. There are many examples of dangerous situations when runners get up too soon and some deaths have occurred in this way as the horns in movement and they strength of the bull means that any goring is more than likely to be mortal.
In this series of photos taken by Maite H. Mateo on the 7th of July, 2012 we can see a good example of how to act. A runner falls in front of the bulls and remains on the ground protecting his head with his hands. Even if the bulls go for him it is difficult for the bull to gore him at such a low height and the runner has most of his important areas of the body reasonably well protected.
With some more pictures from Maite H. Mateo from the 7th of July, 2011 we can see how a reckless runner in a yellow T-shirt causes a small pile-up because he did not stay down on the ground until everything had passed.