if there's grass on the field play ball 

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

if there's grass on the field play ball by Laura Owen September 20, 2008

If there's grass on the field, play ball

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.

If there's grass on the field, play ball by Interex March 19, 2004

If there's grass on the field, play ball

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!"

If there's grass on the field, play ball by Azi0056 February 17, 2019