Is this the supply line and shut off for a sink and dish washer or Ice maker by chance?
What sould have been on there was a simple compression shut off with 1/2 copper on the supply side and a double 3/8 compression for the outgoing water.
All that stuff you have needs to go in the trash and the supply lines changed to stainless steel supplys.
Someones trying to use those cheap gray plastic compression fittings that always leak or just blow off, and the pipe nipple coming into it is under stress and is at an angle and looks like plastic. No real plumber would have used any of that stuff. And lastly that gray and blue tubing has to go.