Sandbox Play is a term that comes from computer RPGS, though it is said to refer back to when war games were played on sandboxes where the wet sand could be shaped into any kind of terrain. It refers to CRPGs where there is no plot that the game is taking the player through, but instead the player is free to roam around the world and interact with it. The player might encounter NPCs who will offer missions, but is free to ignore them or abandon the mission in the middle if it’s too hard or boring; the player can also just instigate things on his own. Grand Theft Auto: Vice City is offered as an example of this style of play (I’ve never played it myself).
By extension in tabletop RPGs Sandbox Play refers to the same sort of qualities in a campaign: no particular overarching plot, with the players free to pursue their own plans and interact with the world as they see fit. There’s no built-in supposition that the players will go on any particular quest or be employed by any particular NPC or organization. There’s some dispute among people who use the term as to whether such things as plot hooks or adventure seeds even exist in Sandbox worlds, but the general consensus seems to be that as long as the players are free to ignore the cries for help, or the reports of trouble brewing in the coastal provinces, it doesn’t diminish the Sandboxness of the setting that it contains such things. In some sense, it’s the essence of the style that such things go on whether or not there are PCs there to interact with them.
Things that are anathema to Sandbox play include: “level appropriate encounters” such that wherever the party goes they only encounter things that they can defeat, but not too easily; Schrodinger’s NPCs, who always are just about to get mugged no matter which alley the PCs are walking by; GMs applying meta-game pressure to the PCs to go on a particular adventure because “this is what I’ve got prepared for this week”; travel that moves at “The Speed of Plot” so that however the PCs choose to travel, and whatever stops they make on the way, they always arrive at the villain’s castle just as the final evil ritual is about to commence. In other words, anything that disturbs the illusion that the game world exists in all its detail and with events proceeding along their course whether or not the PCs are looking in that direction.
Pretty much anybody who’s played in one of my campaigns will recognize this as my default style of GMing (one-offs are a completely different kettle of fish, since they are usually defined by the particular story the PCs are caught up in and end as soon as it’s resolved). Certainly I’ve done things at various times that have violated the spirit of the Sandbox, out of laziness or because the players have started to flounder and asked to be gaffed with a plot hook, but basically Sandbox Play is what I like to GM for anything reasonably long-term.
I think part of it is that I don’t seem to be very good at the overarching plot style of campaign. While I certainly admire the aesthetic of the Sandbox, I’m not married to it. But when I’ve tried the plot-driven campaign (because my players have asked for one)….it doesn’t seem to work out very well. Frankly, their characters usually take one look at the set-up and run away. I don’t know…maybe I’m not very good at conveying the scope of the problem they’re facing versus the extent of the character’s powers, so they think it’s overwhelming or insoluble. My players will sometimes say it’s because “we suuuuuck” but they don’t really believe that, and neither do I. It’s true that my games often feature large-scale unintended consequences, but that’s a reason for caution, not outright paralysis. I mean, it certainly doesn’t paralyse them in the Sandbox campaigns…they just think twice about doing anything major and sometimes prepare contingency plans, then scramble to pick up the pieces if something unforseen occurs. But somehow when it comes to a campaign with a built-in plot from on high, they chicken out.
Now, one thing I haven’t yet tried is making such a campaign set-up do-or-die. The Sandboxer is strong enough in me that when the characters have fled their destiny, I’ve shrugged and let them run, coming up with new stuff in the setting in whichever direction they’ve bugged out. Their destiny has never come and dragged them back kicking and screaming. Maybe it should. It could be that I’ve been confusing character reluctance to buckle down and follow the course of duty with player reluctance to embark on the campaign. I certainly don’t want to force the players down the path of a long and complex adventure if it doesn’t seem fun to them, but maybe once in a while they want to be railroaded–at least to kick off the campaign.