1. to be a sport
2. to go along and do what you are supposed to
From Reservoir Dogs :

(talking about tipping and the fact that tips are taxed)

Mr Pink: (...) Look, if you show me a piece of paper that says the government shouldn't do that, I'll sign it, put it to a vote, I'll vote for it, but what I won't do is play ball. (...)

Meaning he will not do like everyone and start tipping waitresses.
by BelgianTake March 9, 2012
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"I'm gonna play ball with Robert tonight."
"Let's get drunk and play ball."
by mlballstar April 6, 2011
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In a relationship in which one partner is polyamorous, the act of the monogamous partner allowing the poly partner to occasionally have sexual relations with other partners. Similar to a “hall pass,” it shows respect, trust, and mutual understanding between the partners. Those who refuse to play ball are frankly immature, possessive, controlling, and often abusive to their partners.
I thought I’d never get to hook up with Bella, but luckily her boyfriend decided to play ball. He’s such a cool and understanding guy.
by 0000101100101000010101011 January 11, 2021
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A term basically saying that it's alright to at least be attracted to a person as long as they've gone past puberty. Obviously "grass" refers to their "bush" or pubic hair. Would typically be applied to, for instance, a girl maybe 13 years old and up. Can often be used in reference to actual sex (intercourse) but not necessarily.
Man#1: What's the youngest chick you would ever be into at your age? I mean what do you think is "okay" to fantasize about?

Man#2: Hey man. Like my coach always said: if there's grass on the field, it's time to play ball.
by Interex March 19, 2004
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if a girl is old enough to have pubic hair (shaved or unshaved) they are old enough to have sex.
Bob: Do you think Mary is old enough to shag?
John: If there's grass on the field play ball
by Grass May 12, 2004
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If an underage girl has reached puberty, she may be considered appropriate for sexual activity. The reference to "grass on the field" is a metaphor for pubic hair, meaning that any girl who has reached sexual maturity, may be an appropriate sex partner.
if there's grass on the field play ball
by Laura Owen September 20, 2006
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Traditionally, used to denote the beginning of (American) baseball season practice anxiously awaited by enthusiasts each springtime: If there was grass growing, then the season had progressed enou gh past winter to start the new season: "play ball!" More recently, it has become a slang inferring statutory laws regarding underage females did not, in practice, realistically apply and that instead, the presence of pubic hair (grass) indicated sufficient maturation to begin sexual activity (play ball).
"I know your sister's only twelve, but I go by baseball, not age, "If there's grass on the field, play ball!"
by Azi0056 February 17, 2019
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