Ground Rule Double

[backerma]

This should be an easy one but it has caused some confusion at our game the other night. On a ground rule double how many bases is given to a runner that is on first at the time? The umpire ruled that because the runner was between second and third when the ball went out of play then by his judgement the runner should score or be allowed three bases. Is this an area open for umpire judgement or should all runners be allowed only two bases?

Thanks.