A friend of mind said he got hurt in a "mass pile on" during rugby practice as a result of a muddy pitch, now when ever the pitch is muddy practice is held inside for "safety concerns"...I know nothing about rugby, so i have several questions what exactly is a "MASS pile on" and how is it caused by something like "Mud" he also said something about a "domino effect of Forwards coming down". Can someone please break this down in layman's termsA friend of mind said he got hurt in a "mass pile on" during rugby practice as a result of a muddy pitch, now when ever the pitch is muddy practice is held inside for "safety concerns"...I know nothing about rugby, so i have several questions what exactly is a "MASS pile on" and how is it caused by something like "Mud" he also said something about a "domino effect of Forwards coming down". Can someone please break this down in layman's terms

A "pile-on" is just a large ruck which gets kind of confused. A mad scramble for a ball on the ground where the players end up falling over and on top of each other. It tends to happen in muddy conditions because the ball is slippery and hard to handle and players have more difficulty keeping their footing. And if one player goes down, he tends to bring others down with him, and so on, and so on ... -- like a line of dominos where one knocks down another in a chain.