Strike, on and off? (3)

I believe the answer is:

tap

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

'strike' is the definition.
(tap can mean to strike or hit)

I can't explain the remainder of the clue.

(Other definitions for tap that I've seen before include "Light touch (hot or cold?)" , "It's called a faucet in America" , "British faucet" , "Draw upon Pat" , "Get money from, strike" .)

I've seen this clue in the Evening Standard.

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