1st and 2nd bunt situation. 3B's responsibilities

The 3B is definitely burdened in this scenario. He must be in position to field a bunt if it is bunted in his direction. He must also be at the bag if the runner takes off to steal 3B. To accomplish both, the 3B will assume a general position that allows him to do both.

The 3B moves in and angles himself so he can guard against both events. The angle gives him the ability to move forward while still seeing the runner.

Now, some other interesting things that can play into the 3B's mindset. Is there a righthanded pitcher on the mound or a lefthanded pitcher on the mound?

Lefties tend to finish to the 3B side while righties tend to finish to the 1B side. This means that the 3B should account for this.

A lefty on the mound will mean that the 3B might want to consider sliding closer to the line while a righty would slide him closer to the "6 hole."

Now, once the ball is bunted it certainly depends what play is on but generally the 3B will leave to field a ball bunted in his direction. Generally, anything bunted hard at the 1B or pitcher the 3B will retreat and hold down the bag. There are many bunt packages that defenses could employ, but this is a general understanding of the bunt situation.

One last caveat, a 3B should never leave his position in a man on 2nd bunt defense. You do not want the runner stealing in behind you. An amateur mistake is to leave too early only to have a runner steal behind the 3B.