Assuming bases loaded, bottom of the ninth inning tie score. If the
batter hits a home run the home team wins by 4 runs, correct? If a
GROUNDS RULE DOUBLE is hit will the home team win by 1 run or two
runs. If not 2 runs why, which rule?

Hi wheatman,

Only the first run scores, except on a home run:

4.09 (b) 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.

4.11 (c) EXCEPTION: If the last batter in a game hits a home run out
of the playing field, the batter runner and all runners on base are
permitted to score, in accordance with the base running rules, and the
game ends when the batter runner touches home plate.

http://www.mlb.com/NASApp/mlb/mlb/official_info/official_rules/start_end_4.jsp


The batter is credited with only a single, unless a home run:

10.07 GAME ENDING HITS (f) Subject to the provisions of 10.07 (g),
when the batter ends a game with a safe hit which drives in as many
runs as are necessary to put his team in the lead, he shall be
credited with only as many bases on his hit as are advanced by the
runner who scores the winning run, and then only if the batter runs
out his hit for as many bases as are advanced by the runner who scores
the winning run. NOTE: Apply this rule even when the batter is
theoretically entitled to more bases because of being awarded an
"automatic" extra base hit under various provisions of Playing Rules
6.09 and 7.05. (g) When the batter ends a game with a home run hit out
of the playing field, he and any runners on base are entitled to
score.

http://www.mlb.com/NASApp/mlb/mlb/official_info/official_rules/official_scorer_10.jsp

Source:
Major League Baseball: Official Rules
http://www.mlb.com/NASApp/mlb/mlb/official_info/official_rules/foreword.jsp


I hope this is helpful. If you have any questions regarding my answer
please don?t hesitate to ask before rating it.

Best wishes,
Rainbow

Perfect answer

So when a batter hits a HR, the team does win by 4, but with a ground
rule double, theoretically they can win by 2, but the runner on 2nd
base does not usually score, so they win by 1.

How can I post it as an answer? I have the official rule #, but there
is no link to post as an answer.

Thank you for the rating and tip.
Best wishes,
Rainbow

HI Sportsdirect,
You and I are just G-A users.  We cannot post answers, something only
bonafide G-A Researchers can do.  They have blue names, which are also
hyperlinks, so you can click on them and see which questions they have
answered.
Myoarin