It is a ball game using a ball similar in shape to the one used in (American) Football. And just like American Football the idea is to get and keep the ball and do things with it. But that is where the similarity ends.
In Rugger you cannot pass the ball forwards.
In Rugger you cannot wear anything that might be seen to be protective, such as body armor, etc.
In Rugger it is understood that there are no cheerleaders or bands required nor allowed to be present.
In Rugger it is understood that as soon as somebody has possession of the ball, he is fair game for any kind of attack you can make as long as the referee doesn't see it and even then it is OK.
After the game, the men all go to the communal bath where they drink beer and sing bawdy songs, sharing the experience of picking the opponent's teeth out of various body parts and wondering where their own teeth have gone.
Rugger players make Football players look like Ballroom dancers.
Rugger players do not follow any rules except: do anything to get the ball, do anything to keep the ball, when all else fails, fall in a heap on top of whoever has the ball and proceed to kick, punch, gouge and bite any body parts you can see. Including your own.
Then go to a pub and drink copious amounts of beer. When the beer gets lumpy, strain it through a sock.
Bert: "Fuck off you bastard and catch this ball. Mwahahaha"
"Where my ruggers at!?"
"Free beer for all the ruggers!"