Sounds like you've bust the ball off the end of the clutch arm (assuming it's a 3-piece setup and not a Verto ).

Simple to check, as long as you've put the clevis pins in the 'wrong way round' facing upwards to allow clear access to the split pin and to push the pin through easily.

If it's internal, pulling the flywheel and changing the clutch in situ is simple enough.  Fiddly, and poor access to get the the retaining bolts, but once the engine mount is undone and the clutch cover is off it's no more difficult than doing it on the floor.  You only need to jack the side of the engine up by a smidge.

Do you still have the throwout stop fitted? Perhaps the locknut has loosened up and it has migrated toward the cover. The movement you see in the clutch arm could just be slack in the pivot pin and ball. Removing the engine is a PITA IMHO. I once changed a release bearing without removing the engine. Its easy enough although it did take most of the all day.

My bet is that it has something to do with the release bearing...  I would check the lever first as Spank suggests but (IME  when the ball goes the clutch will still work...albeit quite badly...

Your symptoms are consistent with a collapsed bearing (BTDT as well ) ....or maybe damage to the release bearing seat that sits in the middle the diaphragm.

WRT to "in car" clutch changes ... everyone tells me its possible.  However, I have never been able to tip the engine up sufficiently.  Something always gets in the way; radiator against the inner guard shroud, diff hitting the subframe, exhaust getting in the way.  By the time you remove all the obstructions you may as well just pull the engine ... especially if you haven't done the ground work and removed the bottom rear wok bolt the last time you had the engine out.

Cheers, Ian

What do you mean exactly when you say it won't "disengage"?

I've had it happen where there's air in the clutch hydraulics and the heat soak from the exhaust and a braided steel clutch hose cause the fluid to expand and pressing the pedal didn't quite do enough as it lacked force, even though it did move some.

What happens when you try to start the car with your foot on the clutch but the car in gear?

Did you possibly break the little ball off the end of the clutch arm?

I’ve done it without removing the engine, you just need to remove the motor mount on the clutch end, then you can raise or lower the engine to access all the cover bolts. A flex head quarter ratchet like from snap on really helps.

I was parked for about an hour and when I jumped into the car, the clutch wouldn't disengage. The pedal went all the way to the floor with very little resistance. The clutch master and slave cylinders seem to be working OK and the clutch arm is moving through its full range. 

Anyone care to give me a diagnosis? Also, when it's time for me to open it up, what's the consensus, do I leave the motor in, or do I take the motor out? I understand the clutch can be replaced w/ the motor in the car, just wondering which is easier as I have never pulled a motor or rebuilt a clutch. All opinions welcome. Thanks!