Would you be better off standing your ground? I don't actually know how massive a bull is but let's say about 1,700 kg. It's coming at you with a velocity of 16 m/s. You got a human who is a decent 93 kg and runs in the opposite direction at 12.517 m/s (he's an olympian 100m runner). Would this decrease the impact rather? I'm thinking about conservation of momentum. The total momentum of the system changes from about 25,600 to 24,600 (compared to standing). It's not that significantly different if he stood there with no momentum but I'm just thinking a bit.