Honour or Death

Many mortal champions regret their rash pride after the valiant challenge they issued is accepted by a creature whose eyes are the eyes of death itself.
At the start of a challenge, the enemy character selected to take on 
the Vampire must take a Leadership test before any blows are 
struck (a character Immune to Psychology is also immune to this 
effect). If the test is failed, the enemy character will change his 
mind and hide in the rear ranks, refusing to fight the Vampire (see 
issuing a Challenge' on page 99 of the Warhammer rulebook). 
("then the combat will proceed as normal, with no challenges
Fought that turn and the Vampire will be free to fight against ay models he is in contact with.