This happened in a game I was umpiring a couple weeks ago. Young man ball.
Bottom of the 7th, 2 outs, runners on first and second, tie score. Left handed batter is up, defense is playing 5 infielders and 3 outfielders.
Batter gets a base hit into the left center gap. Runner at second scores easily. Game over or is it?
Center fielder runs over, fields the ball and throws it toward the third base dugout as the home team was running out to celebrate a walk-off. The throw hits a player in tne foot as he’s standing in the entrance to their dugout. The other teams proceeds to start vociferously arguing obstruction, blocked ball, lead runner should be out.
What would be your call?

1) Had the lead runner on 2nd already scored? If so, then then the runner on first could be declared out, but the run would count, game over.

2) Was the person struck outside the dugout. Standing at the opening doesn't mean he was in the field of play. If he wasn't in the field of play, then it is a dead ball and all runners advance bases from their position at the time of the release of the thrown ball. Run scores, game over.

3) He was in the field of play and not the on deck batter or base coach. Again, had the run already scored. If not, you have interference, dead ball, runner closest to home is out.

This is based off USSSA rules since you said young guys playing so I presume it wasn't Senior Softball.

Answers:
1) Yes, the runner had legally scored before the ball struck the individuals foot
2) From my vantage point the individual that was struck was standing in the entrance to the dugout.
3) Can’t really say he was on the field. But your second sentence is correct.

You’re also correct that this was not senior softball. Although I umpired u-trip for a lot of years I currently umpire for One Nation. Rules for this situation are pretty much the same across the board for young man’s ball.

For senior ball I defer to BJ or Donna.

Seems absurd that someone would throw the ball like that, but you did say it was not a "mature" men's game. Trying to make that argument would be embarrassing to me; you lost, he came through, tip your hat. However, One thing to think of is if the other baserunners don't get to the next base, the force out is still in effect. If they are celebrating and not paying attention, you could get a force out which would negate the run and the batter would be out on a fielder's choice. But in this case the force out at third is not in effect because the runner on second scored. Throwing it to 3rd was a illogical thing to do but we know how frustrated ballplayers don't always make sound decisions. Now that you explained it, if the force out is not an option, the next time someone hits a walk off base hit against me, I'll get the ball and aim for people celebrating :)

Scott, it was a Mens E tournament and I totally agree with your sentiments. Young kids, many of whom feel their s—- doesn’t stink. Since that play I’ve come to learn from several players that particular outfielder does this fairly often and actually practices it.
I’ll have to check the One Nation rule book but USSSA did have a rule that states you cannot intentionally do that. It’s umpire judgement.