These photos are of an officer trained in hand-to-hand combat.  The officer figured, due to his size and fighting skills, he could disarm a knife wielding aggressor. This is vivid proof of how deadly people who are "only armed with a knife" can be.  Some of the public think that officers should try to disarm someone armed with a knife but anyone who has had training in knife fighting will tell you - even if you win you are going to get cut. 

Keep this in the back of your mind when confronting someone armed with an edged weapon.