ball caught by offensive player

[shipwreck]

Any ruleset. Base runner standing on third when ball is hit. Ball is hit right at the runner. In a reactionary move, he catches the ball while in contact with third. He then realizes what he did and kinda drops, tosses the ball down and heads home to score. What should happen? I believe I know, but the umpires called dead ball, brought him back to third and put the batter on first. On this play does the postion of the nearest defensive player have any bearing on the outcome? Please site what ruleset you are using and the rule infraction. Dave