This is true for open field areas and then A will get away in every situation as the velocity of both agents is equal. But if both agents are restricted by constraints (like a wall in buildings, terrain obstacles or rules (like in Soccer or American Football where players have to stay on the pitch) then the question will be relevant. The last method using a forward vector + something like a velocity factor is the best practical solution. 8 or 10 years ago i have used a mathematical solution based on trigonometry in a XNA app but that creates perhaps too much overhead. By the way the whole scenario is analyzed by Timothy Gay in “The Physics of Football”.