English: “Your hand shall be first upon him” — This teaches that it is a mitzvah for the one who was enticed to put him to death first, and afterward the hand of every person.
On the daf / in context: The person who was the target of the mesis’s words is given the primary duty of initiating the execution; only then does the rest of the people join.
Type of Learning
Derash on the verse (Sifrei) — priority of the intended victim in the execution.
What Is Learned
The one who was enticed must strike first; only afterward does the rest of the people participate.