really? they seem to just try to drown her because they attack each other too sometimes!
mating looks like drowning, male climbs on top, he is heavier so she sinks down, generally he holds her head/neck down, but will let her go when it's done and swim away
I don't doubt that they attack each other if you have 4 males on one pond and only one girl... each male needs his own flock of girls really