This is another idiom related to sports that can also be
used in many situations.  To
settle a score with someone means to “get even” with someone or to
“even up a score.”  If you are playing a
game or sport with someone, you want to win, right?  If you don’t win, you would at least like to
have a tie or be “even”.  Maybe you lose
one match, then you when another match and you have “settled” or “evened up the
score.”  It can be used in a good natured
and fun way, such as when two fans are talking together, as in Example One
below.  It can also be used in a more
sinister way, as in Example Two below.
Example One:
Frank:  I hope that
the Ducks win the pennant this year. 
They got beaten so badly by the Penguins last year, and they are playing
against them again in the finals.
Joe:  Yeah, I would
really like them to settle the score with those Penguins once and for all!  Go Ducks!
Frank:  Yep!  Go Ducks! 
Quack Quack!
In the above example,
the idiom is used literally in the terms of the scores that sports teams play
for.  The Ducks’ fan wants to get even
with the other team; he wants his team to have a higher score and to beat the
Penguins.  Therefore, he wants to”settle
the score” by being victorious over the other team.
Example Two:
Defense Attorney: 
Your honor, my client is completely innocent!  He did not kill his wife’s lover!
Prosecutor:  That
isn’t true, you are lying!  We know that
your client did indeed murder his wife’s lover, and we have the evidence to
prove it!
Defense Attorney: 
That is ridiculous!  What would
his motive possibly be?
Prosecutor:  Why, to
settle a score, of course!  He
knew that his wife was sleeping with your client, and he wanted to get back at
her and get even by killing her lover! 
Isn’t it obvious?  It was for
revenge!

In the second example,
the husband is accused of killing his wife’s lover.  He wants to extract revenge on both of them,
and to punish both of them.  Therefore,
he “settles the score” by murdering his wife’s lover.  Now he feels like he is “even” with both of
them for what they have done to him.

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