In League Play, at least at PC, there are tons of players trolling around with combat knifes. Option 1 is that they're bad and your team becomes trash, or option 2 they're good and just suck because you are always getting knifed from the back. Knifes make League Play unplayable, so please remove the combat knife, at least from League play.
There is no league play for black ops, do you mean black ops 2/3/4? if so here is the links for them:
Hope this helps.