I've been fairly confused about kamma in Theravada, i barely see it mentioned.

Is kamma more like;

1. A person slaps somebody and because of that, they are more likely to be slapped or something similar at some point in the future of their existence?

or

2. A person slaps somebody, and because of that, that same person will be more inclined to slap more people in the future, and have less of a resistance on their actions of slapping people?

or

3. something else? if so, please elaborate