I had this happen last night. Runner on third, batter hits foul ball down the third baseline. The ball was going to be clearly foul, the runner picks up the ball and then throws it back to the pitcher. I called the runner out.
To follow up second guessing my decesion, the LL rulebook mentions fair ball touched by runner before infielder is out.
Two questions for everyone.
1.)Is the pitcher considered an infielder?
2.) Is runner out for touching foul ball before ball has passed first or third?