Have you ever played on a server where it's knife after gun-kill? They have mods that automatically kick your weapon out if it isn't "your level" gun. Server rules are as follows:

One gun-kill per round then you must knife, unless on nade/para level.

If you find your next gun on the floor, you may also use it.

No shoot-knifing - if you run out of bullets you MUST reload.

No interrupting knife fights; if players are "dancing/have hit their target" you must wait to shoot them, or knife them.

You MAY throw a nade into a knife fight.