It's not easy being a Dungeon Master...
Part rules lawyer, storyteller, and arbiter of justice in the game, there are a ton of moving parts to manage leading to a successful game for the evening. And that is before we even factor in the players into the equation. What happens when a player, or even a few of them go off script- really off script and become murder hobos. Player characters wandering around the world attacking anything and everything they see for the experience and treasure. There are lots of ways to "play" Dungeons & Dragons, and I guess one could run a game of vagabond killers, BUT for the most part when a player plays like this if it isn't dealt with, it will quickly destroy the game. Especially troubling for the Dungeon Master given the time and effort one has put into planning and executing the adventure.
When I encounter this type of player I first stop and take a look at where they are coming from- without any intended disrespect. Do they even know what Dungeons & Dragons is? D&D had gone mainstream, which is a good thing, but being mainstream means all types of players find a seat at the adventuring table. And for most the only frame of reference to the game, is approaching it like an analog MMO. Min/max. Powercreep. Best stats and classes. Leveling up as the only point. The gear grind.
As a community Wizards, tried that-it was called D&D 4.0. Perhaps the new player(s) just need an intro to D&D? If I'm starting a campaign with some real neophytes I'll make sure the first adventure as an intro has minimal combat- most of it will be role playing and skill checks, story checks, followed by a single intro combat. But, even experienced players can sometimes get a little attack crazy... In all my games as a DM I am truly open world- play and race, class, alignment you want, go and do what you want in the adventure- no linear adventures which can be very confusing for players.
Do what you want. BUT. There are consequences. Run around attacking people for no reason and soon a bounty will be on your head. Other adventurers will be coming for YOU and the party. Before a player goes all murder hobo I'll let them know, a gentle reminder, that the game world is dynamic, and reputation and actions effect events.
Keep that in mind.
Your thoughts on dealing with players like this?