партнер по поединкам
Context: The speaker was jokingly mentioning someone he often has spars with.
The why of using the preposition "по" does not come naturally to me: "a partner for quarrels"? Could it be that "партнер" often, if not always, takes "по" as a preposition?
As an aside: Does "партнер по поединку" in the dative singular work just as well?