Castigado sin salir

[ROBINDESBOIS]

Si llegas tarde serás castigado sin salir.
How do I translate castigdo sin salir?
Grounded
Punished

[Rusty]

grounded

[ROBINDESBOIS]

And sin salir or does it imply grounded sin salir?

[JPablo]

Yes, it is implied.

grounded
not allowed to go out, forced to stay in...
Pam was grounded for a week because she stayed out all night.

Longman gives 3 definitions for "grounded" (3 is the one that applies)
1. reasonable and in control of your emotions, even when this is difficult
2. someone who is grounded understands their own character and knows what is really important:
Simmons says that her family keeps her grounded.
3. someone, especially a child, who is grounded is kept indoors as a punishment

[Rusty]

castigar sin salir = (to) ground, (to) be grounded