Meaning of 切りかかるなら初手だったね


Context: One of the antagonists comes into the room and they talk with one of
the other characters for a while. As the antagonist turns around and is about
to leave, one of the other characters takes out their sword and tries to
attack her. She uses her magic to reflect the attack and they are sent flying
across the room and then she responds with:

> 切りかかるなら初手だったね

Is she saying that if he was going to try and attack her, he should have done
it at the start or does this mean something else?

Thanks.

Edit: If it is of any help [here is a link to a video which contains the
scene](https://youtu.be/AVUgj8Aq1f0?t=620). The scene is from the 10:20 point
to 10:50. This video contains spoilers for the game ルフランの地下迷宮と魔女ノ旅団.




Your understanding is correct. "(Your attack) must have been at the beginning
(before I noticed it)". 初手 primarily means "the first move" in a game like
chess, go, shogi.

