A prisoner, group of prisoners (heretofore known as a gang) or confederacy thereby having been known to be so tough in their sanctions against unaffiliated or hostile members per se that others remark upon the ponderance of their visage, that they indeed "Run the Yard".
In layman's parlance, this
person or persons are so tough that they control a territory many believe indefensible and do so
day after day, an example of a place indefensible being the aforementioned prison yard, a locale often thought of as having no intrinsic law and with little chance of the uplifting and common practice thereof.
In common talk, a
person or persons that are tough and command the
respect of opposing groups to the point those groups cede territory to the dominant
person or persons.
Dorroile, upon his arrival at the keep, was alarmed to
learn that atramentous
men run the yard, for Dorroile was of an inimical progeny.