CP7 - The "Hold Up"
One side leads, the other deliberately plays low in both hands
  Dummy
♥ 6 2
 
Lead (W)
K Q J 10 5
  East
♥ 9 4 3
  Declarer
♥ A 4 2
 
This is the classic hold up scenario, where the Defenders hold 8 cards in a suit against a NT contract.
To guard against a 5-3 split, Declarer must hold up twice (if he can), and win the 3rd trick with his ♥A. This removes all three hearts held by East.

Provided Declarer now loses any other tricks only to East, West's remaining two heart winners remain isolated and can not be cashed in.
(If Defenders' hearts are split 4-4, Declarer will always lose 3 trick in the suit.)

When the Defence holds 7 cards in a suit, Declarer must hold up once to guard against a 5-2 split.


The Bath Coup
  Dummy
  a. ♥ 6 2
      b. ♥ A 6 2
 
Lead (W)
K Q 10 9 5
  East
   a. ♥ 7 4 3
b. ♥ 7 3
  Declarer
a. ♥ A J 8
b. ♥ J 8 4
 

A standard Opening lead in NT. When holding both the Ace and the Jack in Defenders' long suit, Declarer must hold up once.
If West now continues with this suit he will lose his ♥Q to the ♥A, or lose his ♥10 to the ♥J. The third trick too will then be won by the Declarer's side.

 
CP8 - Avoidance play
to keep the dangerous Opponent off the lead
  Dummy
♠ 8 4 ..
♥ .. ..
♦ A Q J 9 2
♣ K Q 7
 
West (Danger man)
♠ K 9 7 3
♥ .. .. J 10 ..
♦ 8 3
♣ 6 4
  East
♠ J 6 5
♥ .. .. ..
K 10 4
♣ J 10 8 2
Contract : 3NT Declarer
♠ A Q 10
♥ .. .. ..
♦ 7 6 5 <
♣ A 9 5 3
 
West has lead hearts three times, Declarer holding up twice and winning the 3rd trick with his ♥A (see CP7).   But West has two more heart winners in his hand, so he is clearly the danger man who should not gain the lead.

Declarer can take two possible finesses, one in spades, one in diamonds. He choses the one that will not give the lead to the Danger man if it fails.
He therefore leads his ♦5 towards Dummy's ♦J. It loses to East's ♦K.

East now leads his ♠5. Declarer must refuse the finesse and win with his ♠A, then cash all remaining winners, making his 9 tricks required.


  Dummy
♦ 8 6 3
 
West
♦ A Q 9 4
  East (Danger man)
♦ J 10 2
  Declarer
♦ K 7 5
 
Here East is the clear Danger man which must be kept off the lead.
For if East wins a trick he can lead through Declarer's unprotected ♦K, which, when captured, will give four tricks to the Defence.