This is a Blob Chess variant match. Blob Chess is like standard chess, except for two restrictions.
#1) You can move a piece only if it is adjacent (horizontally, vertically, or diagonally) to another one of your pieces before you move it.
#2) The piece you move must land on a square that is adjacent (horizontally, vertically, or diagonally) to another one of your pieces.
Long distance checks are allowed.
Two ways to win:
#1) blob-mate (when the opposing king cannot legally get out of check)
#2) immobilize all your opponent's pieces. (Stalemate = a win).
See here for more details:
http://wiki.schemingmind.com/BlobChessSince we're playing this on a Standard engine, mistakes can happen. Should this happen, contact Mel-o-rama, and he will moderate by suggesting a compensating move or by requesting the errant player to resign.
In case of blob-mate or immobilization (a legal win not recognized by the engine), the loser must resign the game.