Pulled the plug on the Grand Prix in Monaco, as the TV company is using it

I believe the answer is:

closed circuit

I'm a little stuck... Click here to teach me more about this clue!

'it' is the definition.
The definition suggests a singular noun which matches the answer.

I cannot understand how the rest of the clue works.

(Other definitions for closed circuit that I've seen before include "Like security cameras" , "Sort of TV" .)

I've seen this clue in the Irish Times.

Want a hint initially instead of a full solution? Install my app