Are you sure you do not mean the National Federation of High Schools, which generally is used for high schools and middle schools. If so, the answer would be as above, two bases from where the runner is at the time of the throw. I don't think any rule book has a ground rule triple.

It also seems you refer to a batted ball, not a thrown ball as the posts above. That would be two bases from the runner position at the time of the pitch, IF the ball goes dead.

I used the National Federation of Softball only because the organization that runs their leagues uses that on their website. I am pretty well sure they mean the NFHSA.
Most of the umpires seem to be inexperienced ASA guys not really interested during the game. You are correct in that there is no such thing as a ground rule triple. I just used that as an example of the quality of umpires that are hired. In the situation I cited was just because he was too lazy to move up that line away from the plate. The fences at this field are about 170-180 ft at best.
Thanks for the answer.

Ground rules are ground rules - specific to the field you're playing on. "Ground Rule Double" is really "Rule Book Double".. I've been on fields with a ground rule triple before - and what you describe could easily be a ground rule on the field you happened to be on.

That said, this scenario you describe doesn't match the OP at all. Apples and Ducks.

Though many an umpire will scoff at the thought, this is absolutely true.

Speaking ASA

The term "ground rule double" is another matter of convenience that is, IMO, inappropriately used in the rules index. The term is not part of the rules or wording.

For that matter, whether it is a double or not is purely up to the scorekeeper and not a matter for an on-field official.

By definition, "ground" rules are specific to the grounds (read field) upon which the game is being played. While many relate to championship play on completely enclosed fields, ground rules are often a very important part of games played on non-enclosed fields.

I've been on fields where the overgrown landscape is approx. 350' away from the plate. A runner could, and has been, rounding 3rd base by the time the ball reaches the high weeded area. Try selling a logical (other then, "it's in the book") reason for sending the runner back to 2nd base because the defense couldn't do their job.

I will often just not recognize the high grass and tell the teams the field is open, keep playing the ball. When someone objects to that at the pre-game meeting, I simply remind them that using the book means that when their runner is rounding 3rd with the tie-breaking winning run and the ball just gets into the high grass, I'm going to be forced to send that runner back if the plate was beyond the 2 base award. They usually aren't too happy with that possibility. :) However, it is their game and I will allow coaches to have input to any special rule needed to play the game.

Point is that the rule book awards x number of bases on plays under the presumption that the field meets championship play requirements as far as being enclosed within the minimum/maximum parameters stated in Rule 2. The "ground" rules are to supplement those rules when those parameters are exceeded or there is an obstruction located within the confines of the playing field that are not standard to the playing field (i.e. rolled tarp, media area, etc.)

So, the possibility of a ground rule triple, while being somewhat remote, could come into play.

Understand, however, that "ground rules" are covered prior to the start of the game and barring a change an in-game change in the environment, should remain the same throughout.

The field that I worked on that had a ground rule triple (and I worked there quite often for a few years) was relatively normal in all aspects but one. It was built next to a ravine in the left field corner. Instead of building a fence there that would have cut off that corner (fence would have been at about a 45 degree angle to the normal left field fence) it was left open. A solid hit down the third base line could roll to approximately the depth that a normal high school left fielder might play ... but if it rolled any further (right on the line or to the left of that) it would most likely hit the downslope, pick up speed and roll into the ravine.

The ground rule was that if the fielder could get to it, play on ... but if it hit that downslope and passed the fielder it was a 3 base award. An umpire could rule a fly ball into that corner a 4-base award at his discretion (if he felt it would have cleared where a normal LF fence would have been) - I never had to make that call.