Mark 14:2

But they said, Not on the feast day, lest there be an uproar of the people.

The chief priests, scribes and rulers decided not to seize or arrest Jesus openly during the feast, for fear it would cause an uproar or riot among the people. Their fear was that many of the people had witnessed His works and believed Him to be a prophet or believed in Him, and would oppose and resist any attempt against Him and against His liberty. Judging open violence unwise, they chose to act by secrecy and treachery instead.

They aimed to have Him executed before the Passover and hurried the trial, wanting Him put to death not during the feast. Delay through the feast week would have calmed the crowd, stirred those who favored Him to speak for Him, and might have led to His release.