I recently worked on several toilet shutoff valves for a customer and had to shut off the main water supply. I found this at the hose bib and turned clockwise but noticed that at the end of the turning it would keep rotating! In fact, it seemed to keep rotating when full open as well(counterclockwise). I assumed this was the shutoff valve.

Beneath this gate valve was a lever valve (not shown) so I turned that off as well. Being a two story house the water drained out in 10 mins or so but I wasn't patient enough to know or learn which one was the main shutoff. One or both did stop the water.

Is the old red gate valve the shutoff and did someone just leave that in when putting in the newer, lever valve?

Could this be a pressure reducing valve? Yikes. I hope not! I turned it fully open before I left.

Sorry about my ignorance!

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You should have also shown the other valve, but from your description, this is a "broken" gate valve and they just left if in place when they installed the new valve.

most likely a NRS gate valve. (non rising stem)
notorious for failing.
the gate has deep threads that the rotating stem screws into which in turn raises the gate.
when turning the other direction the threads extract from the gate which pushes the gate downward until it seals.
possibly the worst design invented since the components are soft brass.

I never knew about NRS gate valves!

Yes, my first thought was that the valve was stuck open and they installed the lever one to resolve the problem. Sorry about the lack of pic for that! If you look at one of the pics, you can kinda see very, very little of the lever valve just below the brown elbow below the NRS (?) valve.

Maybe I'll check it out again next time I'm there.

Thanks!

VERY few "residential" gate valves are "rising stem".