I know where there is a Subaru Legacy. For sale that has its clutch pedal down on the floor. I can pull it up by hand, but there is no resistance when I push it down again, I do not see a fluid reservoir. Is it cable operated? What might cause this situation?

It should be hydraulic, and the reservoir should be nestling on the "firewall".

 

Serious air in the system will cause this. Or a leak in either end...master or slave cylinder.

 

OR, unlikely, but also more costly to repair..the link arm inside the bell housing is broken or unhinged.