A number of other posts, including one of mine, have examples. Imagine if one player had every single death. He would have a KD of 0 and everyone else would have an infinite KD. The average KD would be infinite. Really bad players can't get a KD less than 0 and thus are limited in the negative impact they can have on the average. Really good players can have KD much higher than 1. The existence of very good players together skews the average greater than 1. If all deaths are credited to someone as kills, it is impossible for this average to be less than 1.