The NFL CBA, the Collective Bargaining Agreement, is in many ways the foundation of the league. Yet it is an odd thing indeed, certainly in the context of what British sport followers might be used to. It is literally a piece of employment law, negotiated sporadically between NFL owners and the NFLPA players’ union, that provides a league-wide employment framework.

That might sound incredibly dry. In some ways, it is. That does not make it any less fundamental to the league, because so many of the league’s workings are on some level dependent on what the players’ employment rights are. Free agency? That’s the players exercising their right to change their employer, and was only introduced in its current guise in the 1993 CBA following numerous legal challenges against restricting player movement. The salary cap? That’s player pay, so obviously an employment issue, and indeed the share of league revenues that goes to the players rather than the owners is a huge part of CBA negotiations. Player practice time? That’s health and safety, so that’s part of employment rights.

The NFL CBA was most recently agreed in 2011, and is set to run until 2020 – there is no set duration, it is negotiated separately each time – but with Colin Kaepernick making at least a token attempt to break the CBA altogether with a lawsuit accusing NFL owners of collusion in not employing him, it feels an opportune moment to look at it and wonder how it might change…

Christian Petersen/Getty Images Sport Start slideshow