The Requirements have been established by Neil Harvey
The majority of the data is in a flat file format which I want to organise properly in a relational database.  

But I’ve continually come up against the problem in tennis and football where the competitors (be they clubs or players) play against each other.  

I came across your design schema yesterday and saw the one for a chess tournament, which I think will help solve my problem. 
 
I would like to understand how to establish the relationship between player_id in table Players and player_id_1 and player_id_2 in table Matches! 

Regards, Neil.