Run an application in an unrooted sandbox on a rooted phone? I have an application that refuses to start on a rooted phone.

I don't want to unroot my phone just for that application; is there any way to run an application inside an unrooted sandbox from a rooted phone (Nexus 5, Stock Android 5.1, rooted)?
You can temporarily disable root access (and then enable it anytime later you want). To do this, there are two most common and simple methods->

1) Turn off root access using the permission manager: Since you are rooted, you must also be using some permission manager like supersu or superuser etc. You can go into its respective settings and disable root access.

2) Turn off root access from Developer Options: Go to Settings-&gt;Developer Options and in the option Root Access select None. This will also disable root access for apps.

Besides these, if it still doesn't work, you can either try completely uninstalling permission manager (this wont unroot you, you can root again anytime by installing them again); or you can simply go to system/bin and system/xbin and delete/move somewhere else a file named su (its the main binary file responsible for root permissions. I suggest you atleast get a backup of it). Further, use these methods only if none of the above two work.