With the NBA lockout over disagreements in revenue sharing with owners and players. The owners are pushing hard for a hard cap and more.  It looks like player salaries are going down to me and if there is no season, the players do not make money. 

I only ask this because I don't know and am curious.  Why can't the players either NBA or NFL just start their own league?  Can someone tell me why this can't be done? 

Both the NBA has the D-League and there's the UFL for Football.  Players get together, get investors, pool money, or whatever.  I know it's better to go with the main league that everyone knows but if owners keep pushing, couldn't they players union have this in their back pocket to threaten the owners back?