Miners were not allowed to fight on pit property, either down in the pit or once above the surface.
Anyone caught fighting would be immediately dismissed. So miners would meet on the fields near the pit brow to settle their disputes.
Apart from no eye gouging or hits to the 'vulnerable' parts of the body, there were no rules.
Bar holds or submission holds, where a wrestler locks his opponent's limb or torso into a position it isn't meant to go in (see the toe-hold above) in other words, going against the bone, were permitted and usually redered the opponent defenseless.
There was however a gentlemen's code which meant that the miners respected the outcome of the fights and each other.
They were hard men
Because of the nature of their labour, the men developed naturally strong physiques; there was no weight training in them days.
They were not muscular like today's wrestlers but strong and wirey all the same.
These men would come out of the pits and wrestle on shale after a hard day's graft: that's how hard they were.
Notes: image source All-in & Catch-as-catch-can wrestling by E.J. Harrison circa 1934