I personally do not get competitive with spar just due to the unstable nature of how lag affects the outcome.
HOWEVER, when I am sparring someone laggy and I stop to type "you are lagging really bad." and they continue to hit me as fast as they can- I view it as scummy. So in my definition that is what a cheap shot is. They seem to get tunnel vision on getting that one additional spar win for their profile rather than following an ethical code of sustaining a reliable connection and allowing someone to talk.
I understand spar is not designated for talking, however when someone talks in spar I do back off and see what they have to say. I don't care much for the win/loss- I am more interested in the fair fight to the end. It is automatically an unfair fight if someone got hit while unable to defend themselves- and that right there shows an inner personality trait of selfishness and unsportsmanship