Acts 6
11 Then they secretly induced men to say, “We have heard him speak blasphemous words against Moses and God.” 12 And they stirred up the people, the elders, and the scribes; and they came upon him, seized him, and brought him to the council. 

So after Stephen beat them down in the debate and they realized his wisdom was unmatched, they decided to take matters into their own hands.

Notes from my commentary:
They secretly induced men to say: The opponents of Stephen could not win a fair fight, so they used lies and secret strategies to shape popular opinion against Stephen.

They stirred up the people: The opponents of Stephen could do nothing against the followers of Jesus until they got popular opinion on their side. Previously, persecution against the apostles had been limited because popular opinion was with them

Popular opinion can be easily shaped. The same crowds that praised Jesus (Luke 19:35-40) soon called for His crucifixion (Luke 23:18-23). The crowds that loved the apostles (Acts 2:475:26) cry out against Stephen. This is why we should never let popular opinion shape the vision or focus of the church, but let it rest on God’s eternal Word.

This could NOT be more true in today’s society.