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Lois: So the cocky billionaire thinks I'll lend him credibility. Believe him?

Grant: Personally I think you're underqulified. Once your emotions take over,
Lex will cross home plate standing. Make her look funny?

Lois: Emotions? I am the girl who didn't cry
during The Notebook. Besides, I will be whipping
so many hardballs... Lex will never see first base.
She'll be so tough on him
that Lex will not be able to sneak out?
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If A lends credibility to B, then A makes B more believable.
B must have something on the ball, because he's a friend of A's.

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I think this is a baseball reference. "Cross home plate standing [up]." (I hope "up" isn't a smiley!)
When you hit a homerun (outside the park) you don't have to worry about being tagged out or forced out. You don't have to slide into the base. You can take your time.
So, once your emotions take over, Lex will [have/then] hit a homerun with you!

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Another baseball analogy. Reaching first base is the batter's first objective. (His ultimate objective is to reach home and score.)
When we say "He never even got to first base with the girl," we mean that his advances were totally rejected.
"Whipping so many hard balls" puts her in the pitcher's position. (I'm afraid "hard balls" is a mixed metaphor here.)
She's throwing so many balls which are very difficult to hit (possibly fast balls) that she strikes him out (causes him to strike out).
The metaphor "playing hardball" compares baseball with softball, implying that softball is for sissies. Hardball (baseball) is the real thing. (possibly, more dangerous - certainly, more serious)
Comments  
Thanks for the thorough explanations, Avangi!Emotion: smile