Metaphor is a mapping between elements of source and target domains. When the mapping arises, rich background knowledge of source elements, which is called metaphorical inference, is mapped onto a target domain, resulting in metaphorical entailment. Since Lakoff and Johnson (1980), the mapping has been considered as being partial. It has been claimed that some of the elements are highlighted in the mapping and others are hidden. However, the partial nature of the metaphorical entailment has not been discussed so far. Bridging the gap, this paper observes the partial nature of metaphorical entailment, conducting the case study with the metaphor LIFE IS A BASEBALL GAME. The detailed investigation of the metaphor reveals that there are four different types of the partial entailment and that the partial nature of the entailment is due to the metonymic highlighting of various inferences.