The responder's 2nd bid after an overcall in a major, a Sputnik and 1NT rebid by the opener.
Analyze the hand of the 1
♦ opener that rebid 1NT after a 1
♠ overcall : He has a regular 1st zone hand (12-14HCP), with :
- 4 or 5 cards in ♦ (opening of his best minor)
- Not 4 cards in ♥, otherwise, he would have shown support after his partner's Sputnik
- Not necessarily a stopper in the overcalled suit (1NT could have been the only possible bid with 2 or 3 small cards in ♠....).
Now, all you have to do is draw the logical conclusions...depending on your hand !
The opener's rebid at 1NT does not guarantee a stopper in the overcalled suit. It may well be the only possible rebid.