shovel, not shove. Shoving isn't bad, that means, for example. pushing your opponent with an arm. shoveling means using a hold-all simple opener to grab your opponent from far below their center of mass and then lift up to make them fall backwards either outside the dojo or on their head inside it, both resulting in DQ.
it can be countered, but it's an unfairly easy way to beat a better opponent. I guess it's not that bad on lower belt servers, but it's really frowned upon on blackbelt servers.