infield fly rule- player leaving the field

Question
bases loaded with one out batter hits fly ball that drops in behind second basemens, Second basemen picks up the ball and throws out the runner moving from first to second (no tag) the runner from third scores. The umpire says runners can advance at own risk and because no tag was made he is sending runner back to second I argued that the runner is out because he left the field and went in the dugout he is out. He said no cause I called him out at first so he is allowed to come back.

Answer
Michael,

I would say the runner heading from first to second would be out for leaving the baseline.  I think the run would count, depending on when the runner from 3rd scored in relation to when the runner heading to second abandoned the baseline.

Hope this helps!

Brian