rugby
Just like in English, we call 'Rugby' in French. It's both a game and a word in French. It's a direct borrowing from English, so there is no change in the spelling. It is used exactly as it would be in English. French people also commonly use this term to discuss about the popular sport 'Rugby'.
I like watching rugby on television.
The given sentence is simply expressing a person's enjoyment of viewing the sport of rugby on television. In French, 'J'aime' means 'I like', 'regarder' means 'to watch', 'le rugby' refers to the sport of rugby, and 'à la télévision' translates to 'on television'.
Rugby is a very physical sport.
This sentence is declaring the physicality of the sport of rugby. In French, 'Le rugby' refers to the sport of rugby, 'est' translates to 'is', 'un sport' means 'a sport', and 'très physique' implies that something is 'very physical'.
He plays rugby every weekend.
This sentence demonstrates a person's habit of playing rugby each weekend. In French, 'Il joue' means 'He plays', 'au rugby' refers to the sport of rugby, and 'tous les weekends' translates to 'every weekend'.