Variable Player Box Size for "Ducking Behavior"

I was wondering if there was any way to shrink the player box in a platformer to match a ducking animation. In other words, if a character ducks under a projecile, the player box is the same so he still would get hit. I would like to know if I need to create a wholly different player object.

Thanks

I'm guessing you have a hitbox for the player and an object for the visual side of the player. If that's true you could just do every tick -> set hitbox size to player size

I would set the height of the hitbox to half of what it normally is when the down key is pressed - example here

dl.dropboxusercontent.com/u/70305965/crouch.capx