Darren Sharper -- HE'S BEING DENIED JUSTICE ... Family Says

Darren Sharper's family believes the former NFL star is being denied basic justice by being held in an L.A. jail despite the fact he already posted bail ... and they're furious ... sources connected to the case tell TMZ Sports.

We're told family members and close friends of the former Saints player -- who was ordered to remain behind bars until the extradition issue with AZ is sorted out -- believe he is confident in proving his innocence and is not afraid to take his case to trial. But they feel the process has started off on an unfair and vengeful footing.

Our sources say Darren's family believes there's no reason he should be locked up like a murderer when he's been cooperative and played by the rules by cooperating with police and turning himself in ... especially since he posted bail last month.

In fact, Sharper's supporters believe the battle over extradition is a dirty tactic to keep him locked up so he'll be painted as a guilty man before any evidence is presented and the trial even starts.