In Arthur Miller's The Crucible, Abigail Williams is the ringleader of the girls involved with the witchcraft accusations.
The best evidence for that comes in act 2 of the play. Mary Warren has just come home from the court proceedings. She is quite late, and John Proctor is not happy about it. Upon entering the Proctor's household, Mary Warren hands Elizabeth Proctor a poppet. The poppet has a needle in it.
Cheever then arrives at the Proctor household to arrest Elizabeth for witchcraft. Abigail had been stabbed in the stomach with a needle. The poppet had a needle stuck in it, so everybody thought that Elizabeth was messing with voodoo or some such nonsense in order to hurt Abigail from afar.
John Proctor finds out that the needle was placed there by Mary earlier, and he tells Mary that she will tell the court how the needle really came to be there. Mary says that she can't because Abigail will kill her.
"Mary Warren: She’ll kill me for sayin’ that! Proctor continues toward her. Abby’ll charge lechery on you, Mr. Proctor!"
Abigail is most definitely the girl leading the charge, and the other girls are following out of fear.