How do I get my 2D punch sprite to cause damage?

I am making a PvP fighter game for a 2D side scroller. I have my punch flipbook setup and it works great, but so far does not have any collision to hit the other player. I tried creating a collision sphere component but I don’t know how to get it to only be active when the character punches, and to be about the size of the hand, and at arm’s length.