This question already has an answer here:
In the campaign I run, it is frequently the case that one player will make an attack against an unsurprised enemy to start combat. For example:
DM: "At the end of the long hall, you see a large door, flanked by two hobgoblins. They are alerted to your presence but do not move."
Ranger: "I shoot at the one on the left with my longbow."
In these situations, no one is surprised, and a party member has specifically stated that they will perform the action that brings us into combat and cues initiative order. But does this affect initiative order?
If everyone just rolls for initiative, then there is a very good chance that someone, maybe even an enemy, will have a higher initiative than the inciting adventurer. But that doesn't make a whole lot of sense when the combat wouldn't happen at all (not yet, anyway) if that adventurer didn't make an attack. And then the player who is playing the ranger feels like his cool idea was ignored when he rolls a crappy initiative.
I realize that those who roll a higher initiative than the inciting adventurer could take a non-combat option, such as Dodge, Help, or Dash, but I don't think the party would be a big fan of reducing the party's attack quantity for the first round..
I was thinking about making a house rule that gives such a player a +5 bonus on their initiative roll or that allows players to choose their initiative as long as it isn't higher than what they rolled or something like that, but is there already a mechanic in place for this kind of situation?