Balk

[Jimmer]

Has there been any instance of a balk being called without a baserunner? 

[maven]

Yes. But it was a mistake.

[noumpere]

From OBR (emphasis added):

 

6.02 Pitcher Illegal Action
(a) Balks
If there is a runner, or runners, it is a balk when:

 

and

 

A BALK is an illegal act by the pitcher with a runner or runners on
base, entitling all runners to advance one base.

[BLWizzRanger]

My SWMBO balks all the time. But that might be me not calling the right pitch.