First and foremost, we need to address the two types of base coaches: A first base coach and a third base coach. Both are equally as important, but their list of duties vary. Here are two lists of duties that each base coach is responsible for:
DUTIES OF A FIRST BASE COACH
1. Calling out foul balls
Of course the umpire will call a foul, but there are times when umpires simply gesture the foul ball motion, or just don't yell loud enough. It is a responsibility of the first base coach to communicate to the batter coming out of the box that they have just hit a foul. This will allow the player to slow their running speed and head back into the batter's box. Don't let the poor kid give it their all running to first on every foul ball, let them conserve their energy. The last thing you want is a worn out player in the batter's box trying to hit.
2. Words of encouragement
Hustle is everything. Once the batter has made contact, encourage them to hustle down the line to first base. Your job as a first base coach is to get them to first base as fast as possible by offering loud words of encouragement. Unless they've just hit one out of the park, players should always be hustling to the base ahead.
3. To round, or not to round, that is the question
It is a necessity that the first base coach communicate with the runner and tell them whether or not they should round first base and head to second, or to stop at first. This is best done by using both verbal communication and hand motions. It is up to you and your team what these gestures should look like.
4. Communicate number of outs
This is a duty that both the first base and third base coach should carry out. Your players on base should already know the number of outs, but remind them anyways. This will ensure that they will know where the play is being made and whether or not they will have to tag up if a fly ball is hit.
5. Let runner on first know when they should tag up
When a pop fly is hit, it is the responsibility of the first base coach to track the ball and to let the runner on first know if they should tag up or run to second. Make sure you communicate this loud and clear.
DUTIES OF A THIRD BASE COACH
1. Give signs to the batter
Signs can be given to the batter by either base coach, but it is typically the responsibility of the third base coach. This is because there are almost always more right-handed batters than lefties. So, the third base coach is positioned closer to most players when they step out of the batter's box between pitches.
2. Communicate number of outs
As mentioned earlier, this is a duty that both the first base and third base coach should carry out. Your players on base should know how many outs there are and where the next play is-- at all times.
3. Let runners on second and third know if they need to tag up
When a ball is hit in the air, it is the responsibility of the third base coach to let the runners on second and third know if they should tag up or if they should advance to the next base. Make sure that you communicate this loud and clear.
4. Tell runners when to slide
Communicating with runners when to slide is a must. The third base coach must be aware where the ball is at all times, where the play is being made, and whether or not the runners going into second, third and home plate should slide into the bag. The runner that takes priority is the one heading towards the base where the play is being made.
5. To round, or not to round, that is the question
Like the first base coach, the third base coach should let players know when to round the bag and head to the next base or when to stop. The third base coach is responsible for runners at both second and third base.