Walk-Off, I think

[umpjim]

Originally Posted by Rich Ives

No.

When the winning run is scored in the last half-inning of a regulation game, or in
the last half of an extra inning, as the result of a base on balls, hit batter or any other
play with the bases full which forces the runner on third to advance, the umpire
shall not declare the game ended until the runner forced to advance from third has
touched home base and the batter-runner has touched first base.

Once F5 touches 3B R3 is no longer forced. It then reverts to the normal "run can't score when" exceptions.

So in the OP, the outfielder without security guard interference could not run down the ball and throw to 3B for a force on a runner who did not advance?