Team Fortress 2 - Image #822,803

close enough

-25hp (Or -2hp per swing)
-Default stats in Wrench mode
-Hit Special Attack button to flip over to Knife mode. Knife has default knife stats. Here you can counter Enemy Spy's knives, disabling them for 4 seconds if you land a hit whilst the enemy Spy has their knife active. Spy can still use other weapons.
-No random critical hits in knife mode
-Cannot backstab
-Cannot penetrate a Razorback in knife mode, doing no damage
Apart from how new players would quickly be confused by the weapon i'd say that balances the idea.