Although the third base coach is the most visible, and most controversial, of the two base coaches, the first base coach in baseball plays a vital role in ensuring the success of baserunners. The first base coach has several vital duties to prevent runners from encountering ill-timed outs on the bases.
Above all else, it is the job of the first base coach to ensure that the runner on first is aware of all situations and possible outcomes on every pitch. The coach must know how many outs there are, what the count is to the batter and whether or not the pitcher is making a pick-off move to first base.
Always be in the ear of the runner. Between pitches, remind him of the number of outs and what he should do in a fly ball or ground ball scenario. If the pitcher makes a pick-off move to first, the coach must yell, "Back!" to ensure the runner knows to retreat to the base. On a batted ball into the outfield, the coach must be sure the batter can hear whether to try for a double or hold to a single.
Situations may arise in which the runner leading off first base can't see what is happening at the plate because the batter is left-handed, shielding the ball from the runner. The first base coach must decide quickly when he sees a passed ball or wild pitch whether or not to send the runner to second base. Any hesitation can force the runner to stay at first. If a ball is hit in the air as a runner is attempting to steal, the first base coach must quickly judge if the ball will be caught and yell for the runner to return. Split seconds can be the difference between a safe call and an out.
Protect Your Player
Often, a batter will reach first base at the same time as the throw from an infielder and the runner will be called out. If the runner believes he has been wrongly called out, his emotions may lead to a confrontation with the umpire. It is the job of the first base coach to intervene and keep the angry player at bay, until the manager can reach the scene. This can prevent a player from getting ejected.