With no runners on base, start in the 'A' position, 10-15 feet behind the baseman. Position yourself according to the baseman and not the base. Stand entirely in foul territory but close enough to the line so that if you pivot around on a ball over your head, you end up straddling the line. Position 'D' is the mirror opposite of position 'A' but is never used in a two man crew. On a three man crew, with no one on base, the third umpire starts in 'D'. The third base umpire alternates between D and C while the first base umpire alternates between A and B depending on the runners. Only one umpire is ever in the field at the start of any play. With a runner on first, go to the 'B' position. Stand roughly halfway between the rubber and second base on an imaginary line drawn from home plate to the edge of the mound circle and beyond. On a short field, stand outside the baseline and 10-15 feet behind the baseman. Based on experience and comfort, you can cheat to the first base side of the imaginary line if you anticipate a pickoff play or a bunt.  If you anticipate a stolen base attempt, step back a few feet if on the inside and come forward a few feet if on the outside. There are only 8 options for the field umpire when considering base runners: 1) No one on base -  A 2) Man on first - B 3) Man on second - C 4) Man on third - C or B ( B with 2 outs) 5) Man on first and second - B 6) Man on first and third - B 7) Man on second and third - C 8) Bases loaded - B If you expect a play, be nearer that base, so you can drift between B and C based on play Position 'C' is the exact mirror to position 'B', just on the other side of the mound.  You would stand there with a runner on second, runners on first and second, and runners on second and third with less than two outs. Best base positions are based on the odds of the next play. If a man on third with two outs, the odds of the next play will be to first base - so be closer, thus B position. Man on first and third, the odds are a play at second either on a steal or lead force = B position.