Casca explains to Brutus and Cassius what happened when Caesar was offered a symbolic crown, how he refused it three times to the cheers of the crowd, and how Casca believes his refusal was not sincere: "but, for all that, to my thinking, he would fain have had it."
He then goes on to explain that Caesar fell to the ground, shaking and foaming at the mouth. "He fell down in the marketplace, and foamed at mouth, and was speechless." Brutus and Cassius explain it is epilepsy, which they refer to as "the falling sickness."
Casca explains that the crowds easily forgave Caesar for his odd behavior, and suggests they would have forgiven him for murdering their mothers, they adored him so. "Three or four wenches where I stood cried, 'Alas, good soul!' and forgave him with all their hearts. But there’s no heed to be taken of them. If Caesar had stabbed their mothers they would have done no less."
We can infer from those comments that Casca is not Caesar's biggest fan... or a fan at all. In the end Cassius invites Casca for dinner sometime, and the audience can assume it is in an attempt to get Casca on the "Down with Caesar!" bandwagon.