If you are shooting a rifle with a scope and the cross hairs get blurry but the target doesn't you don't have the scope adjusted properly. With a scope the target and cross hairs are on the same plane, they should both be in focus at the same time. It's like looking at a picture of your target with cross hairs on it.

I don't think your reticle is adjusted properly. Or if you are using a scope with fixed parallax you may be using too much magnification for the distance you are shooting.

Paul