What makes one a combatant?

[Van Silke]

In other words, what makes one participate in (or enter) combat?

In case of "a combatant is in an initiative order" answer, steps of entering combat say, that "when combat begins, all combatants roll initiative". So, you need to be a combatant in the first place to have an initiative order.

I'm largely confused and need to know, because I can't find any direct clause that says when a character becomes a combatant/enters combat.

[SlimGauge]

I would say that "all combatants roll initiative" means "all *potential* combatants". Any creature that *could* be involved in the combat.

[CrystalSeas]

Any character who is in range of another character's (or NPC or monster) attacks is a combatant.

Even bystanders are combatants if they have the potential to respond to attacks being made.

If you are just idly standing there, and an arrow hits you, the GM needs to know when your turn is. You explain your response to that attack on your turn in the initiative.

[Van Silke]

Thanks. That clarifies things a little bit.