BBC Sport t Russell Fuller looks at the key questions after a players' union co-founded by Novak Djokovic began legal action against tennis' governing bodies.

The Professional Tennis Players Association, along with 22 players, have filed multiple lawsuits in several countries against the ATP, WTA, ITF, and ITIA. The suit alleges that those international tennis organizations have engaged in anticompetitive business practices that suppress their potential earnings and cast aside health and safety concerns,