Here's the short summary:
Basically, it would be exactly like the football (ball), with a model of a knife and a few slight changes.
Changes:
1: The model. The model would be thin, and about as big as the football and not any bigger than the football. The model would also look like
http://i.imgur.com/KLJSAQT.png.
2: Issues with the ball: Unlike the ball, you would be able to keep it in your inventory. Also, you would have to make it so that it does not kill you when you step on it to pick it up (maybe you could code it so that if it stood still for like a second it would turn into item form and you could pick it up?). Also it will instakill.
Other than the things I just listed, nothing will be changed.
If you want to get serious about this, you can add me on steam here -
http://steamcommunity.com/profiles/76561198042516841/and you can add me on skype, my username is "gunter.datguy22".