Straddling the foul line

[justanotherump]

I've never heard taught to be in fair at first base.
Professional baseball used to instruct to be in fair territory with a runner on third, if the third base umpire is on the line. This was to see all things at the plate, foul or foul tip in the dirt, check swing, ball off the bat, etc. you will be three or four paces, minimum, behind the third baseman, so hot shots down the line shouldn't be too much of a problem. Though it could still happen.