Examples:

• What? Maybe you don't know this, but they are playing for keeps.
• I don't know if you can understand this, but they're playing for keeps.
• And that's playing for keeps, is it?
• Okay, guys, just remember, in the real world, you'll be playing for keeps.
• That means he's playing for keeps.
• She's playing for keeps, you've gotta do the same.
• Oh, easily these boys are playing for keeps.
• I'm playing for keeps.
• Think he forgot he was playing for keeps and with someone else's dough.
• Yeah, she was playing for keeps.