Around the 1870s, the idea grew up of charging a small premium to members of the audience who were willing to arrive well ahead of the crowd and avoid the crush; in return, they were allowed to choose their own seats in unreserved areas - the pit and the gallery in particular. This could be a considerable advantage, as sightlines in those areas were often poor or interrupted by pillars. The earliest comment on the practice I’ve found is this:
It was with some degree of satisfaction that I welcomed a movement in the right direction adopted at most of our local theatres during the pantomime season - namely that of providing special entrances or early doors for the convenience of those who, wishing to avoid the crush, would willingly pay a small extra amount.
[Liverpool Mercury, 24 Apr. 1877.] ....
somebody in the football world in the UK - identity now lost - later remembered the expression and reinvented it to refer figuratively to the early part of a game.
The name of Ron Atkinson, TV football commentator, has been linked to the phrase.